diff --git a/openapi-bal-service/src/main/java/io/ballerina/openapi/converter/Constants.java b/openapi-bal-service/src/main/java/io/ballerina/openapi/converter/Constants.java
index 310ccc379..d1a2a97c7 100644
--- a/openapi-bal-service/src/main/java/io/ballerina/openapi/converter/Constants.java
+++ b/openapi-bal-service/src/main/java/io/ballerina/openapi/converter/Constants.java
@@ -238,5 +238,8 @@ public String toString() {
     public static final String YML_EXTENSION = ".yml";
     public static final String PLUS = "+";
     public static final String UNDERSCORE = "_";
-
+    public static final String HTTP_202 = "202";
+    public static final String HTTP_400 = "400";
+    public static final String ACCEPTED = "Accepted";
+    public static final String BAD_REQUEST = "BadRequest";
 }
diff --git a/openapi-bal-service/src/main/java/io/ballerina/openapi/converter/service/OpenAPIRequestBodyMapper.java b/openapi-bal-service/src/main/java/io/ballerina/openapi/converter/service/OpenAPIRequestBodyMapper.java
index 9308f66e3..8a278cbe3 100644
--- a/openapi-bal-service/src/main/java/io/ballerina/openapi/converter/service/OpenAPIRequestBodyMapper.java
+++ b/openapi-bal-service/src/main/java/io/ballerina/openapi/converter/service/OpenAPIRequestBodyMapper.java
@@ -283,8 +283,8 @@ private String getMediaTypeForSyntaxKind(TypeDescriptorNode payloadNode) {
                 return customMediaPrefix == null ? MediaType.APPLICATION_OCTET_STREAM :
                         APPLICATION_PREFIX + customMediaPrefix + OCTECT_STREAM_POSTFIX;
             case SIMPLE_NAME_REFERENCE:
-                SimpleNameReferenceNode record = (SimpleNameReferenceNode) payloadNode;
-                TypeSymbol typeSymbol = getReferenceTypeSymbol(semanticModel.symbol(record));
+            case QUALIFIED_NAME_REFERENCE:
+                TypeSymbol typeSymbol = getReferenceTypeSymbol(semanticModel.symbol(payloadNode));
                 if (typeSymbol instanceof TypeReferenceTypeSymbol) {
                     typeSymbol = ((TypeReferenceTypeSymbol) typeSymbol).typeDescriptor();
                 }
@@ -346,16 +346,21 @@ private void handleArrayTypePayload(Map<String, Schema> schema, ArrayTypeDescrip
         TypeDescriptorNode typeDescriptorNode = arrayNode.memberTypeDesc();
         // Nested array not allowed
         io.swagger.v3.oas.models.media.MediaType media = new io.swagger.v3.oas.models.media.MediaType();
-        if (typeDescriptorNode.kind().equals(SyntaxKind.SIMPLE_NAME_REFERENCE)) {
+        if (typeDescriptorNode.kind().equals(SyntaxKind.SIMPLE_NAME_REFERENCE) ||
+                typeDescriptorNode.kind().equals(SyntaxKind.QUALIFIED_NAME_REFERENCE)) {
             //handle record for components
-            SimpleNameReferenceNode referenceNode = (SimpleNameReferenceNode) typeDescriptorNode;
-            TypeSymbol typeSymbol = getReferenceTypeSymbol(semanticModel.symbol(referenceNode));
+            TypeSymbol typeSymbol = getReferenceTypeSymbol(semanticModel.symbol(typeDescriptorNode));
             OpenAPIComponentMapper componentMapper = new OpenAPIComponentMapper(components);
             componentMapper.createComponentSchema(schema, typeSymbol);
             diagnostics.addAll(componentMapper.getDiagnostics());
             Schema itemSchema = new Schema();
-            arraySchema.setItems(itemSchema.$ref(ConverterCommonUtils.unescapeIdentifier(
-                    referenceNode.name().text().trim())));
+            String referenceName;
+            if (typeDescriptorNode.kind().equals(SyntaxKind.SIMPLE_NAME_REFERENCE)) {
+                referenceName = ((SimpleNameReferenceNode) typeDescriptorNode).name().toString().trim();
+            } else {
+                referenceName = ((QualifiedNameReferenceNode) typeDescriptorNode).identifier().text();
+            }
+            arraySchema.setItems(itemSchema.$ref(ConverterCommonUtils.unescapeIdentifier(referenceName)));
             media.setSchema(arraySchema);
         } else if (typeDescriptorNode.kind() == SyntaxKind.BYTE_TYPE_DESC) {
             StringSchema byteSchema = new StringSchema();
diff --git a/openapi-bal-service/src/main/java/io/ballerina/openapi/converter/service/OpenAPIResponseMapper.java b/openapi-bal-service/src/main/java/io/ballerina/openapi/converter/service/OpenAPIResponseMapper.java
index b9c3f0242..c10a14045 100644
--- a/openapi-bal-service/src/main/java/io/ballerina/openapi/converter/service/OpenAPIResponseMapper.java
+++ b/openapi-bal-service/src/main/java/io/ballerina/openapi/converter/service/OpenAPIResponseMapper.java
@@ -61,6 +61,7 @@
 import io.ballerina.openapi.converter.utils.ConverterCommonUtils;
 import io.ballerina.tools.diagnostics.Location;
 import io.swagger.v3.oas.models.Components;
+import io.swagger.v3.oas.models.Operation;
 import io.swagger.v3.oas.models.headers.Header;
 import io.swagger.v3.oas.models.media.ArraySchema;
 import io.swagger.v3.oas.models.media.ComposedSchema;
@@ -92,7 +93,9 @@
 import static io.ballerina.compiler.syntax.tree.SyntaxKind.RECORD_FIELD;
 import static io.ballerina.compiler.syntax.tree.SyntaxKind.SIMPLE_NAME_REFERENCE;
 import static io.ballerina.compiler.syntax.tree.SyntaxKind.TYPE_REFERENCE;
+import static io.ballerina.openapi.converter.Constants.ACCEPTED;
 import static io.ballerina.openapi.converter.Constants.APPLICATION_PREFIX;
+import static io.ballerina.openapi.converter.Constants.BAD_REQUEST;
 import static io.ballerina.openapi.converter.Constants.BODY;
 import static io.ballerina.openapi.converter.Constants.BYTE;
 import static io.ballerina.openapi.converter.Constants.BYTE_ARRAY;
@@ -105,7 +108,9 @@
 import static io.ballerina.openapi.converter.Constants.HTTP_200_DESCRIPTION;
 import static io.ballerina.openapi.converter.Constants.HTTP_201;
 import static io.ballerina.openapi.converter.Constants.HTTP_201_DESCRIPTION;
+import static io.ballerina.openapi.converter.Constants.HTTP_202;
 import static io.ballerina.openapi.converter.Constants.HTTP_204;
+import static io.ballerina.openapi.converter.Constants.HTTP_400;
 import static io.ballerina.openapi.converter.Constants.HTTP_500;
 import static io.ballerina.openapi.converter.Constants.HTTP_500_DESCRIPTION;
 import static io.ballerina.openapi.converter.Constants.HTTP_CODES;
@@ -197,8 +202,13 @@ public void getResourceOutput(FunctionDefinitionNode resource, OperationAdaptor
         } else {
             // When the return type is not mention in the resource function.
             ApiResponse apiResponse = new ApiResponse();
-            apiResponse.description("Accepted");
-            apiResponses.put("202", apiResponse);
+            apiResponse.description(ACCEPTED);
+            apiResponses.put(HTTP_202, apiResponse);
+            if (operation.getRequestBody() != null || operation.getParameters() != null) {
+                ApiResponse badRequestResponse = new ApiResponse();
+                badRequestResponse.description(BAD_REQUEST);
+                apiResponses.put(HTTP_400, badRequestResponse);
+            }
         }
         operation.setResponses(apiResponses);
     }
@@ -433,7 +443,17 @@ private Optional<ApiResponses> getAPIResponses(OperationAdaptor operationAdaptor
         io.swagger.v3.oas.models.media.MediaType mediaType = new io.swagger.v3.oas.models.media.MediaType();
         String statusCode = httpMethod.equals(POST) ? HTTP_201 : HTTP_200;
         String description = httpMethod.equals(POST) ? HTTP_201_DESCRIPTION : HTTP_200_DESCRIPTION;
-
+        if (typeNode.parent().kind() == SyntaxKind.OPTIONAL_TYPE_DESC) {
+            ApiResponse acceptedRequestResponse = new ApiResponse();
+            acceptedRequestResponse.description(ACCEPTED);
+            apiResponses.put(HTTP_202, acceptedRequestResponse);
+            Operation operation = operationAdaptor.getOperation();
+            if (operation.getRequestBody() != null || operation.getParameters() != null) {
+                ApiResponse badRequestResponse = new ApiResponse();
+                badRequestResponse.description(BAD_REQUEST);
+                apiResponses.put(HTTP_400, badRequestResponse);
+            }
+        }
         String mediaTypeString;
         switch (typeNode.kind()) {
             case QUALIFIED_NAME_REFERENCE:
@@ -790,11 +810,11 @@ private static void addResponse(ApiResponses apiResponses, Optional<ApiResponses
         apiResponse.ifPresent(responses -> responses.forEach((key, value) -> {
             if (apiResponses.containsKey(key)) {
                 ApiResponse res = apiResponses.get(key);
-                Content content = res.getContent();
-                if (content == null) {
-                    content = new Content();
-                }
                 if (value.getContent() != null) {
+                    Content content = res.getContent();
+                    if (content == null) {
+                        content = new Content();
+                    }
                     String mediaType = value.getContent().keySet().iterator().next();
                     Schema newSchema = value.getContent().values().iterator().next().getSchema();
                     if (content.containsKey(mediaType)) {
@@ -813,8 +833,8 @@ private static void addResponse(ApiResponses apiResponses, Optional<ApiResponses
                     } else {
                         content.put(mediaType, value.getContent().values().iterator().next());
                     }
+                    res.content(content);
                 }
-                res.content(content);
                 apiResponses.put(key, res);
             } else {
                 apiResponses.put(key, value);
diff --git a/openapi-cli/src/test/java/io/ballerina/openapi/generators/openapi/DataTypeTests.java b/openapi-cli/src/test/java/io/ballerina/openapi/generators/openapi/DataTypeTests.java
index 2adb42fab..b5d0caa4d 100644
--- a/openapi-cli/src/test/java/io/ballerina/openapi/generators/openapi/DataTypeTests.java
+++ b/openapi-cli/src/test/java/io/ballerina/openapi/generators/openapi/DataTypeTests.java
@@ -50,14 +50,12 @@ public void testForAllTypeDefinitions() throws IOException {
     @Test(description = "When the record field has type definitions with nullable")
     public void testForAllTypeDefinitionWithNullableValue() throws IOException {
         Path ballerinaFilePath = RES_DIR.resolve("data_type/nullable_type_def.bal");
-        //Compare generated yaml file with expected yaml content
         TestUtils.compareWithGeneratedFile(ballerinaFilePath, "data_type/nullable_type_def.yaml");
     }
 
     @Test(description = "test for tuple type scenarios")
     public void testForTupleType() throws IOException {
         Path ballerinaFilePath = RES_DIR.resolve("data_type/tuple_types.bal");
-        //Compare generated yaml file with expected yaml content
         TestUtils.compareWithGeneratedFile(ballerinaFilePath, "data_type/tuple_type.yaml");
     }
 
diff --git a/openapi-cli/src/test/java/io/ballerina/openapi/generators/openapi/NegativeResponseTests.java b/openapi-cli/src/test/java/io/ballerina/openapi/generators/openapi/NegativeResponseTests.java
new file mode 100644
index 000000000..ceea47c6b
--- /dev/null
+++ b/openapi-cli/src/test/java/io/ballerina/openapi/generators/openapi/NegativeResponseTests.java
@@ -0,0 +1,66 @@
+/*
+ *  Copyright (c) 2023, WSO2 LLC. (http://www.wso2.org).
+ *
+ *  WSO2 LLC. licenses this file to you under the Apache License,
+ *  Version 2.0 (the "License"); you may not use this file except
+ *  in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing,
+ *  software distributed under the License is distributed on an
+ *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ *  KIND, either express or implied.  See the License for the
+ *  specific language governing permissions and limitations
+ *  under the License.
+ */
+package io.ballerina.openapi.generators.openapi;
+
+import io.ballerina.openapi.cmd.OASContractGenerator;
+import org.testng.Assert;
+import org.testng.annotations.AfterMethod;
+import org.testng.annotations.AfterTest;
+import org.testng.annotations.BeforeMethod;
+import org.testng.annotations.Test;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+
+/**
+ * This test class is covering the negative unit tests for return type scenarios.
+ */
+public class NegativeResponseTests {
+    private static final Path RES_DIR = Paths.get("src/test/resources/ballerina-to-openapi").toAbsolutePath();
+    private Path tempDir;
+
+    @BeforeMethod
+    public void setup() throws IOException {
+        this.tempDir = Files.createTempDirectory("bal-to-openapi-test-out-" + System.nanoTime());
+    }
+
+    @Test(description = "When the resource has nil type return")
+    public void testNilReturnType() {
+        Path ballerinaFilePath = RES_DIR.resolve("response/negative/nil_return_type.bal");
+        OASContractGenerator openApiConverterUtils = new OASContractGenerator();
+        openApiConverterUtils.generateOAS3DefinitionsAllService(ballerinaFilePath, this.tempDir, null
+                , false);
+        //TODO: Uncomment after merging this PR https://github.com/ballerina-platform/openapi-tools/pull/1370.
+//        Assert.assertFalse(openApiConverterUtils.getErrors().isEmpty());
+        Assert.assertFalse(Files.exists(tempDir.resolve("payloadV_openapi.yaml")));
+    }
+
+
+    @AfterMethod
+    public void cleanUp() {
+        TestUtils.deleteDirectory(this.tempDir);
+    }
+
+    @AfterTest
+    public void clean() {
+        System.setErr(null);
+        System.setOut(null);
+    }
+}
diff --git a/openapi-cli/src/test/java/io/ballerina/openapi/generators/openapi/ResponseTests.java b/openapi-cli/src/test/java/io/ballerina/openapi/generators/openapi/ResponseTests.java
index 2916d3f6f..66b0de8c8 100644
--- a/openapi-cli/src/test/java/io/ballerina/openapi/generators/openapi/ResponseTests.java
+++ b/openapi-cli/src/test/java/io/ballerina/openapi/generators/openapi/ResponseTests.java
@@ -373,6 +373,26 @@ public void testResponseHasServiceConfigWithCorsWithoutBasePath() throws IOExcep
         Assert.assertTrue(generatedYaml.contains(expectedYamlContent));
     }
 
+    @Test(description = "When the resource has nil type return")
+    public void testNilReturnType() throws IOException {
+        Path ballerinaFilePath = RES_DIR.resolve("response/nil_return_type.bal");
+        OASContractGenerator openApiConverterUtils = new OASContractGenerator();
+        openApiConverterUtils.generateOAS3DefinitionsAllService(ballerinaFilePath, this.tempDir, null
+                , false);
+        Assert.assertTrue(openApiConverterUtils.getErrors().isEmpty());
+        compareWithGeneratedFile(ballerinaFilePath, "response/nil_return_type.yaml");
+    }
+
+    @Test(description = "When the resource has nil union type return")
+    public void testNilUnionReturnType() throws IOException {
+        Path ballerinaFilePath = RES_DIR.resolve("response/nil_union_return_type.bal");
+        OASContractGenerator openApiConverterUtils = new OASContractGenerator();
+        openApiConverterUtils.generateOAS3DefinitionsAllService(ballerinaFilePath, this.tempDir, null
+                , false);
+        Assert.assertTrue(openApiConverterUtils.getErrors().isEmpty());
+        compareWithGeneratedFile(ballerinaFilePath, "response/nil_union_return_type.yaml");
+    }
+
     @AfterMethod
     public void cleanUp() {
         TestUtils.deleteDirectory(this.tempDir);
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/advance/openapi/multiple_service_01.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/advance/openapi/multiple_service_01.yaml
index 04b0ed714..d1013a597 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/advance/openapi/multiple_service_01.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/advance/openapi/multiple_service_01.yaml
@@ -20,4 +20,6 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components: {}
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/advance/openapi/multiple_service_02.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/advance/openapi/multiple_service_02.yaml
index 64b03b69f..42cf1986d 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/advance/openapi/multiple_service_02.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/advance/openapi/multiple_service_02.yaml
@@ -20,4 +20,6 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components: {}
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/advance/openapi/multiple_service_03.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/advance/openapi/multiple_service_03.yaml
index 1afb02252..0246abab0 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/advance/openapi/multiple_service_03.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/advance/openapi/multiple_service_03.yaml
@@ -20,4 +20,6 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components: {}
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/ballerina-project/service/snowpeak_request_body.bal b/openapi-cli/src/test/resources/ballerina-to-openapi/ballerina-project/service/snowpeak_request_body.bal
index 63440d66d..30c48aea6 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/ballerina-project/service/snowpeak_request_body.bal
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/ballerina-project/service/snowpeak_request_body.bal
@@ -31,6 +31,15 @@ service /payloadV on new http:Listener(9090) {
         return created;
     }
 
+    # Represents Snowpeak reservations resource
+    #
+    # + reservations - Array representation of Reservations
+    # + return - `ReservationCreated` or ReservationConflict representation
+    resource function post reservations(@http:Payload rep:Reservation[] reservations)
+                returns @http:Cache{} http:Created|rep:ReservationConflict {
+        return http:CREATED;
+    }
+
     # Represents Snowpeak payment resource
     #
     # + id - Unique identification of payment
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/apidoc/path_param.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/apidoc/path_param.yaml
index c2e6618c2..40b0f2b03 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/apidoc/path_param.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/apidoc/path_param.yaml
@@ -24,4 +24,6 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components: {}
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/apidoc/query_param.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/apidoc/query_param.yaml
index 7dc0c56c0..4032141cc 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/apidoc/query_param.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/apidoc/query_param.yaml
@@ -36,4 +36,6 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components: {}
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/apidoc/record.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/apidoc/record.yaml
index c5436da83..8dfafdb44 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/apidoc/record.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/apidoc/record.yaml
@@ -23,6 +23,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components:
   schemas:
     ReserveRoom:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/apidoc/requestBody.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/apidoc/requestBody.yaml
index c5436da83..8dfafdb44 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/apidoc/requestBody.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/apidoc/requestBody.yaml
@@ -23,6 +23,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components:
   schemas:
     ReserveRoom:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/apidoc/typeInclusion.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/apidoc/typeInclusion.yaml
index 8d6c50401..a3610e89b 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/apidoc/typeInclusion.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/apidoc/typeInclusion.yaml
@@ -21,6 +21,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components:
   schemas:
     Link:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/enum.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/enum.yaml
index c08e915a1..ad068be5f 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/enum.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/enum.yaml
@@ -23,6 +23,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
   /getOrder:
     post:
       operationId: postGetorder
@@ -34,6 +36,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components:
   schemas:
     Link:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/enum_array_type.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/enum_array_type.yaml
index 7d46388bd..528d6ee1f 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/enum_array_type.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/enum_array_type.yaml
@@ -23,6 +23,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components:
   schemas:
     Link:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/enum_with_value.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/enum_with_value.yaml
index 649707787..4d3ebb060 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/enum_with_value.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/enum_with_value.yaml
@@ -23,6 +23,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components:
   schemas:
     Link:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/nullable_type_def.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/nullable_type_def.yaml
index 69b43b99d..033912d25 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/nullable_type_def.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/nullable_type_def.yaml
@@ -23,6 +23,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components:
   schemas:
     Salary:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/tuple_type.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/tuple_type.yaml
index 4c73b825e..b3d86631d 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/tuple_type.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/tuple_type.yaml
@@ -21,6 +21,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components:
   schemas:
     User:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/type_def.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/type_def.yaml
index 9a90a7b61..cc725d4d7 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/type_def.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/data_type/type_def.yaml
@@ -23,6 +23,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
   /reservation/{id}:
     get:
       operationId: getReservationId
@@ -35,6 +37,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components:
   schemas:
     PriceMap:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/escape_identifier.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/escape_identifier.yaml
index f52b498b4..c2e6addb0 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/escape_identifier.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/escape_identifier.yaml
@@ -52,6 +52,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components:
   schemas:
     Pet-Task:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/escape_identifier_02.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/escape_identifier_02.yaml
index 464e8e273..f8ac76f1b 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/escape_identifier_02.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/escape_identifier_02.yaml
@@ -97,6 +97,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
     put:
       operationId: putพิมพ์ชื่อ
       parameters:
@@ -108,6 +110,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components:
   schemas:
     ErrorPayload:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/json/nestedRecord.json b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/json/nestedRecord.json
index fae643d56..ee2cce824 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/json/nestedRecord.json
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/json/nestedRecord.json
@@ -31,6 +31,9 @@
         "responses" : {
           "202" : {
             "description" : "Accepted"
+          },
+          "400" : {
+            "description" : "BadRequest"
           }
         }
       }
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/path_scenario03.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/path_scenario03.yaml
index 23a3a2e63..7a12d0318 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/path_scenario03.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/path_scenario03.yaml
@@ -1,4 +1,14 @@
-
+openapi: 3.0.1
+info:
+  title: PayloadV
+  version: 0.0.0
+servers:
+  - url: "{server}:{port}/payloadV"
+    variables:
+      server:
+        default: http://localhost
+      port:
+        default: "9090"
 paths:
   /:
     get:
@@ -24,4 +34,6 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components: {}
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/path_scenario04.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/path_scenario04.yaml
index 987d24857..11696f1c4 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/path_scenario04.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/path_scenario04.yaml
@@ -23,6 +23,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
     post:
       operationId: post
       responses:
@@ -46,4 +48,6 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components: {}
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/readonly.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/readonly.yaml
index 2f6b7fd4b..dd02de00b 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/readonly.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/readonly.yaml
@@ -40,6 +40,10 @@ paths:
           schema:
             type: string
       responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
         "200":
           description: Ok
           content:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/record/typeInclusion.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/record/typeInclusion.yaml
index 5848bc863..2e0c01eff 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/record/typeInclusion.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/record/typeInclusion.yaml
@@ -21,6 +21,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components:
   schemas:
     Link:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/json_payload.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/json_payload.yaml
index 5b5361e17..0d3466549 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/json_payload.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/json_payload.yaml
@@ -1,3 +1,14 @@
+openapi: 3.0.1
+info:
+  title: PayloadV
+  version: 0.0.0
+servers:
+  - url: "{server}:{port}/payloadV"
+    variables:
+      server:
+        default: http://localhost
+      port:
+        default: "9090"
 paths:
   /hi:
     post:
@@ -9,5 +20,6 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components: {}
-
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/mime_with_record_payload.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/mime_with_record_payload.yaml
index 655fb6b49..2b21461c7 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/mime_with_record_payload.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/mime_with_record_payload.yaml
@@ -1,3 +1,14 @@
+openapi: 3.0.1
+info:
+  title: PayloadV
+  version: 0.0.0
+servers:
+  - url: "{server}:{port}/payloadV"
+    variables:
+      server:
+        default: http://localhost
+      port:
+        default: "9090"
 paths:
   /hi:
     post:
@@ -10,6 +21,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components:
   schemas:
     Pet:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/multiple_payload.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/multiple_payload.yaml
index 2de5acd84..b89bd81ba 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/multiple_payload.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/multiple_payload.yaml
@@ -1,3 +1,14 @@
+openapi: 3.0.1
+info:
+  title: PayloadV
+  version: 0.0.0
+servers:
+  - url: "{server}:{port}/payloadV"
+    variables:
+      server:
+        default: http://localhost
+      port:
+        default: "9090"
 paths:
   /hi:
     post:
@@ -11,4 +22,6 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components: {}
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/nested_2record.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/nested_2record.yaml
index 763a8edfb..8abcdab4c 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/nested_2record.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/nested_2record.yaml
@@ -1,3 +1,14 @@
+openapi: 3.0.1
+info:
+  title: PayloadV
+  version: 0.0.0
+servers:
+  - url: "{server}:{port}/payloadV"
+    variables:
+      server:
+        default: http://localhost
+      port:
+        default: "9090"
 paths:
   /hi:
     post:
@@ -10,6 +21,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components:
   schemas:
     Tag:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/nested_array.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/nested_array.yaml
index bb686a16f..d314c6e45 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/nested_array.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/nested_array.yaml
@@ -1,3 +1,14 @@
+openapi: 3.0.1
+info:
+  title: PayloadV
+  version: 0.0.0
+servers:
+  - url: "{server}:{port}/payloadV"
+    variables:
+      server:
+        default: http://localhost
+      port:
+        default: "9090"
 paths:
   /hi:
     post:
@@ -10,6 +21,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components:
   schemas:
     Pet:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/nested_record.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/nested_record.yaml
index beaa3bddb..80a37f845 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/nested_record.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/nested_record.yaml
@@ -1,3 +1,14 @@
+openapi: 3.0.1
+info:
+  title: PayloadV
+  version: 0.0.0
+servers:
+  - url: "{server}:{port}/payloadV"
+    variables:
+      server:
+        default: http://localhost
+      port:
+        default: "9090"
 paths:
   /hi:
     post:
@@ -10,6 +21,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components:
   schemas:
     Dog:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/record_field_array.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/record_field_array.yaml
index af27e8b47..310e82985 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/record_field_array.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/record_field_array.yaml
@@ -1,3 +1,14 @@
+openapi: 3.0.1
+info:
+  title: PayloadV
+  version: 0.0.0
+servers:
+  - url: "{server}:{port}/payloadV"
+    variables:
+      server:
+        default: http://localhost
+      port:
+        default: "9090"
 paths:
   /hi:
     post:
@@ -10,6 +21,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components:
   schemas:
     Dog:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/record_payload.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/record_payload.yaml
index 655fb6b49..2b21461c7 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/record_payload.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/record_payload.yaml
@@ -1,3 +1,14 @@
+openapi: 3.0.1
+info:
+  title: PayloadV
+  version: 0.0.0
+servers:
+  - url: "{server}:{port}/payloadV"
+    variables:
+      server:
+        default: http://localhost
+      port:
+        default: "9090"
 paths:
   /hi:
     post:
@@ -10,6 +21,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components:
   schemas:
     Pet:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/union_type.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/union_type.yaml
index 72172bab0..c425d1324 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/union_type.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/request_body/union_type.yaml
@@ -21,6 +21,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
   /path1:
     post:
       operationId: postPath1
@@ -40,6 +42,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
   /path3:
     post:
       operationId: postPath3
@@ -55,6 +59,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
   /path4:
     post:
       operationId: postPath4
@@ -71,6 +77,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
   /path5:
     post:
       operationId: postPath5
@@ -85,6 +93,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
   /path6:
     post:
       operationId: postPath6
@@ -100,6 +110,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
   /path7:
     post:
       operationId: postPath7
@@ -117,6 +129,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
   /path8:
     post:
       operationId: postPath8
@@ -134,6 +148,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
   /path9:
     post:
       operationId: postPath9
@@ -152,6 +168,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
 components:
   schemas:
     ABC:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/response/cache_config_06.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/response/cache_config_06.yaml
index d8751ee2b..2d17c0d93 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/response/cache_config_06.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/response/cache_config_06.yaml
@@ -58,6 +58,8 @@ paths:
             text/plain:
               schema:
                 type: string
+        "202":
+          description: Accepted
         "500":
           description: Internal server error
           content:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/response/nil_return_type.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/response/nil_return_type.yaml
new file mode 100644
index 000000000..55d3ba79a
--- /dev/null
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/response/nil_return_type.yaml
@@ -0,0 +1,330 @@
+openapi: 3.0.1
+info:
+  title: PayloadV
+  version: 0.0.0
+servers:
+  - url: "{server}:{port}/payloadV"
+    variables:
+      server:
+        default: http://localhost
+      port:
+        default: "9090"
+paths:
+  /path1:
+    get:
+      operationId: getPath1
+      responses:
+        "202":
+          description: Accepted
+    put:
+      operationId: putPath1
+      responses:
+        "202":
+          description: Accepted
+    post:
+      operationId: postPath1
+      responses:
+        "202":
+          description: Accepted
+    delete:
+      operationId: deletePath1
+      responses:
+        "202":
+          description: Accepted
+    head:
+      operationId: headPath1
+      responses:
+        "202":
+          description: Accepted
+    patch:
+      operationId: patchPath1
+      responses:
+        "202":
+          description: Accepted
+  /path_with_query:
+    get:
+      operationId: getPathWithQuery
+      parameters:
+        - name: id
+          in: query
+          required: true
+          schema:
+            type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+    put:
+      operationId: putPathWithQuery
+      parameters:
+        - name: id
+          in: query
+          required: true
+          schema:
+            type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+    post:
+      operationId: postPathWithQuery
+      parameters:
+        - name: id
+          in: query
+          required: true
+          schema:
+            type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+    delete:
+      operationId: deletePathWithQuery
+      parameters:
+        - name: id
+          in: query
+          required: true
+          schema:
+            type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+    head:
+      operationId: headPathWithQuery
+      parameters:
+        - name: id
+          in: query
+          required: true
+          schema:
+            type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+    patch:
+      operationId: patchPathWithQuery
+      parameters:
+        - name: id
+          in: query
+          required: true
+          schema:
+            type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+  /path_with_path/{id}:
+    get:
+      operationId: getPathWithPathId
+      parameters:
+        - name: id
+          in: path
+          required: true
+          schema:
+            type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+    put:
+      operationId: putPathWithPathId
+      parameters:
+        - name: id
+          in: path
+          required: true
+          schema:
+            type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+    post:
+      operationId: postPathWithPathId
+      parameters:
+        - name: id
+          in: path
+          required: true
+          schema:
+            type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+    delete:
+      operationId: deletePathWithPathId
+      parameters:
+        - name: id
+          in: path
+          required: true
+          schema:
+            type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+    head:
+      operationId: headPathWithPathId
+      parameters:
+        - name: id
+          in: path
+          required: true
+          schema:
+            type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+    patch:
+      operationId: patchPathWithPathId
+      parameters:
+        - name: id
+          in: path
+          required: true
+          schema:
+            type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+  /path_with_headers:
+    get:
+      operationId: getPathWithHeaders
+      parameters:
+        - name: header
+          in: header
+          required: true
+          schema:
+            type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+    put:
+      operationId: putPathWithHeaders
+      parameters:
+        - name: header
+          in: header
+          required: true
+          schema:
+            type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+    post:
+      operationId: postPathWithHeaders
+      parameters:
+        - name: header
+          in: header
+          required: true
+          schema:
+            type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+    delete:
+      operationId: deletePathWithHeaders
+      parameters:
+        - name: header
+          in: header
+          required: true
+          schema:
+            type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+    head:
+      operationId: headPathWithHeaders
+      parameters:
+        - name: header
+          in: header
+          required: true
+          schema:
+            type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+    patch:
+      operationId: patchPathWithHeaders
+      parameters:
+        - name: header
+          in: header
+          required: true
+          schema:
+            type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+  /path_with_request_body:
+    put:
+      operationId: putPathWithRequestBody
+      requestBody:
+        content:
+          text/plain:
+            schema:
+              type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+    post:
+      operationId: postPathWithRequestBody
+      requestBody:
+        content:
+          text/plain:
+            schema:
+              type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+    delete:
+      operationId: deletePathWithRequestBody
+      requestBody:
+        content:
+          text/plain:
+            schema:
+              type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+    patch:
+      operationId: patchPathWithRequestBody
+      requestBody:
+        content:
+          text/plain:
+            schema:
+              type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+components: {}
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/response/nil_union_return_type.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/response/nil_union_return_type.yaml
new file mode 100644
index 000000000..73850c720
--- /dev/null
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/response/nil_union_return_type.yaml
@@ -0,0 +1,223 @@
+openapi: 3.0.1
+info:
+  title: PayloadV
+  version: 0.0.0
+servers:
+  - url: "{server}:{port}/payloadV"
+    variables:
+      server:
+        default: http://localhost
+      port:
+        default: "9090"
+paths:
+  /path_get_error:
+    get:
+      summary: for `get` method with nil return type and error
+      operationId: getPathGetError
+      responses:
+        "202":
+          description: Accepted
+        "500":
+          description: Internal server error
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/ErrorPayload'
+  /path_get:
+    get:
+      summary: for `get` method with nil return type and success status code
+      operationId: getPathGet
+      responses:
+        "202":
+          description: Accepted
+        "200":
+          description: Ok
+          content:
+            text/plain:
+              schema:
+                type: string
+  /path_get_query_param:
+    get:
+      summary: for `get` method with nil return type and success status code with
+        query param
+      operationId: getPathGetQueryParam
+      parameters:
+        - name: id
+          in: query
+          required: true
+          schema:
+            type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+        "200":
+          description: Ok
+          content:
+            text/plain:
+              schema:
+                type: string
+  /path_post:
+    post:
+      summary: for `post` method with 201 payload with error status code and nil type
+      operationId: postPathPost
+      responses:
+        "201":
+          description: Created
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Links'
+        "202":
+          description: Accepted
+        "404":
+          description: NotFound
+  /path:
+    get:
+      summary: for union return type with error status code and nil type
+      operationId: getPath
+      responses:
+        "200":
+          description: Ok
+          content:
+            text/plain:
+              schema:
+                type: string
+        "202":
+          description: Accepted
+        "404":
+          description: NotFound
+    post:
+      summary: "resource has 3 status codes that explicitly returns (202, 404, 400)\
+        \ while ? type returns implicitly 400, 202"
+      operationId: postPath
+      parameters:
+        - name: id
+          in: query
+          required: true
+          schema:
+            type: string
+      responses:
+        "202":
+          description: Accepted
+        "404":
+          description: NotFound
+        "400":
+          description: BadRequest
+          content:
+            text/plain:
+              schema:
+                type: string
+  /path_with_query:
+    get:
+      summary: "resource has 4 status codes that explicitly returns (200, 404) while\
+        \ ? type returns implicitly 400, 202"
+      operationId: getPathWithQuery
+      parameters:
+        - name: id
+          in: query
+          required: true
+          schema:
+            type: string
+      responses:
+        "200":
+          description: Ok
+          content:
+            text/plain:
+              schema:
+                type: string
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+        "404":
+          description: NotFound
+  /path_with_path/{id}:
+    post:
+      summary: "resource has 3 status codes that explicitly returns (404) while ?\
+        \ type returns implicitly 400, 202"
+      operationId: postPathWithPathId
+      parameters:
+        - name: id
+          in: path
+          required: true
+          schema:
+            type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+        "404":
+          description: NotFound
+  /path_with_headers:
+    post:
+      summary: "method has 3 status codes that explicitly returns (404) while ? type\
+        \ returns implicitly 400, 202"
+      operationId: postPathWithHeaders
+      parameters:
+        - name: header
+          in: header
+          required: true
+          schema:
+            type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+        "404":
+          description: NotFound
+  /path_with_request_body:
+    post:
+      operationId: postPathWithRequestBody
+      requestBody:
+        content:
+          text/plain:
+            schema:
+              type: string
+      responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
+        "404":
+          description: NotFound
+components:
+  schemas:
+    ErrorPayload:
+      type: object
+      properties:
+        reason:
+          type: string
+          description: Reason phrase
+        path:
+          type: string
+          description: Request path
+        method:
+          type: string
+          description: Method type of the request
+        message:
+          type: string
+          description: Error message
+        timestamp:
+          type: string
+          description: Timestamp of the error
+        status:
+          type: integer
+          description: Relevant HTTP status code
+          format: int32
+    Links:
+      required:
+        - id
+        - links
+      type: object
+      properties:
+        id:
+          type: integer
+          format: int64
+        links:
+          type: array
+          items:
+            type: string
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/response/rs_scenario09.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/response/rs_scenario09.yaml
index 85d69033c..95763776e 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/response/rs_scenario09.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/response/rs_scenario09.yaml
@@ -28,6 +28,8 @@ paths:
       responses:
         "202":
           description: Accepted
+        "400":
+          description: BadRequest
     put:
       operationId: putHi
       responses:
@@ -59,6 +61,10 @@ paths:
             type: integer
             format: int64
       responses:
+        "202":
+          description: Accepted
+        "400":
+          description: BadRequest
         "500":
           description: Internal server error
           content:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/response/rs_scenario20.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/response/rs_scenario20.yaml
index 6df8c5ba0..3f1b4f773 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/response/rs_scenario20.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/response/rs_scenario20.yaml
@@ -20,6 +20,8 @@ paths:
             '*/*':
               schema:
                 description: Any type of entity body
+        "202":
+          description: Accepted
         "500":
           description: Internal server error
           content:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/snowpeak_request_body_ref.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/snowpeak_request_body_ref.yaml
index 22fdfebfd..ad6cfdf69 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/snowpeak_request_body_ref.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/snowpeak_request_body_ref.yaml
@@ -44,6 +44,38 @@ paths:
             text/plain:
               schema:
                 type: string
+  /reservations:
+    post:
+      summary: Represents Snowpeak reservations resource
+      operationId: postReservations
+      requestBody:
+        description: Array representation of Reservations
+        content:
+          application/json:
+            schema:
+              type: array
+              items:
+                $ref: '#/components/schemas/Reservation'
+      responses:
+        "201":
+          description: Created
+          headers:
+            Cache-Control:
+              schema:
+                type: string
+                default: "must-revalidate,public,max-age=3600"
+            ETag:
+              schema:
+                type: string
+            Last-Modified:
+              schema:
+                type: string
+        "409":
+          description: Conflict
+          content:
+            text/plain:
+              schema:
+                type: string
   /payment/{id}:
     post:
       summary: Represents Snowpeak payment resource
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/status_code/not_acceptable.yaml b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/status_code/not_acceptable.yaml
index ccf554b4b..7b4a878fd 100644
--- a/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/status_code/not_acceptable.yaml
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/expected_gen/status_code/not_acceptable.yaml
@@ -16,6 +16,8 @@ paths:
       responses:
         "406":
           description: NotAcceptable
+        "202":
+          description: Accepted
         "500":
           description: Internal server error
           content:
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/response/negative/nil_return_type.bal b/openapi-cli/src/test/resources/ballerina-to-openapi/response/negative/nil_return_type.bal
new file mode 100644
index 000000000..50cd00198
--- /dev/null
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/response/negative/nil_return_type.bal
@@ -0,0 +1,11 @@
+import ballerina/http;
+
+service /payloadV on new http:Listener(9090) {
+
+     resource function get path_with_request_body(@http:Payload string payload) {
+     };
+
+     resource function head path_with_request_body(@http:Payload string payload) {
+     };
+
+}
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/response/nil_return_type.bal b/openapi-cli/src/test/resources/ballerina-to-openapi/response/nil_return_type.bal
new file mode 100644
index 000000000..eb9a1bf03
--- /dev/null
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/response/nil_return_type.bal
@@ -0,0 +1,76 @@
+import ballerina/http;
+
+service /payloadV on new http:Listener(9090) {
+    resource function get path1() {
+    };
+    resource function get path_with_query(string id)  {
+    };
+    resource function get path_with_path/[string id]() {
+    };
+    resource function get path_with_headers(@http:Header string header) {
+    };
+
+    resource function post path1() {
+    };
+    resource function post path_with_query(string id)  {
+    };
+    resource function post path_with_path/[string id]() {
+    };
+    resource function post path_with_headers(@http:Header string header) {
+    };
+    resource function post path_with_request_body(@http:Payload string payload) {
+    };
+
+    resource function put path1() {
+    };
+    resource function put path_with_query(string id)  {
+    };
+    resource function put path_with_path/[string id]() {
+    };
+    resource function put path_with_headers(@http:Header string header) {
+    };
+    resource function put path_with_request_body(@http:Payload string payload) {
+    };
+
+    resource function patch path1() {
+    };
+    resource function patch path_with_query(string id)  {
+    };
+    resource function patch path_with_path/[string id]() {
+    };
+    resource function patch path_with_headers(@http:Header string header) {
+    };
+    resource function patch path_with_request_body(@http:Payload string payload) {
+    };
+
+    resource function delete path1() {
+    };
+    resource function delete path_with_query(string id)  {
+    };
+    resource function delete path_with_path/[string id]() {
+    };
+    resource function delete path_with_headers(@http:Header string header) {
+    };
+    resource function delete path_with_request_body(@http:Payload string payload) {
+    };
+
+    resource function head path1() {
+    };
+    resource function head path_with_query(string id)  {
+    };
+    resource function head path_with_path/[string id]() {
+    };
+    resource function head path_with_headers(@http:Header string header) {
+    };
+
+    resource function option path1() {
+    };
+    resource function option path_with_query(string id)  {
+    };
+    resource function option path_with_path/[string id]() {
+    };
+    resource function option path_with_headers(@http:Header string header) {
+    };
+    resource function option path_with_request_body(@http:Payload string payload) {
+    };
+}
diff --git a/openapi-cli/src/test/resources/ballerina-to-openapi/response/nil_union_return_type.bal b/openapi-cli/src/test/resources/ballerina-to-openapi/response/nil_union_return_type.bal
new file mode 100644
index 000000000..e45f14226
--- /dev/null
+++ b/openapi-cli/src/test/resources/ballerina-to-openapi/response/nil_union_return_type.bal
@@ -0,0 +1,53 @@
+import ballerina/http;
+
+type Links record {|
+    int id;
+    string[] links;
+|};
+
+ public type BadRequestRecord record {|
+    *http:BadRequest;
+    string body;
+ |};
+
+
+service /payloadV on new http:Listener(9090) {
+    # for `get` method with nil return type and error
+    resource function get path_get_error() returns error? {
+    };
+
+    # for `get` method with nil return type and success status code
+    resource function get path_get() returns string? {
+    };
+
+    # for `get` method with nil return type and success status code with query param
+    resource function get path_get_query_param(string id) returns string? {
+    };
+
+    # for `post` method with 201 payload with error status code and nil type
+    resource function post path_post() returns Links|http:NotFound? {
+    };
+
+    # for union return type with error status code and nil type
+    resource function get path() returns string|http:NotFound? {
+    };
+
+    # resource has 3 status codes that explicitly returns (202, 404, 400) while ? type returns implicitly 400, 202
+    resource function post path(string id) returns http:Accepted|http:NotFound|BadRequestRecord? {
+    };
+
+    # resource has 4 status codes that explicitly returns (200, 404) while ? type returns implicitly 400, 202
+    resource function get path_with_query(string id) returns string|http:NotFound? {
+    };
+
+    # resource has 3 status codes that explicitly returns (404) while ? type returns implicitly 400, 202
+    resource function post path_with_path/[string id]() returns http:NotFound? {
+    };
+
+    # method has 3 status codes that explicitly returns (404) while ? type returns implicitly 400, 202
+    resource function post path_with_headers(@http:Header string header) returns http:NotFound? {
+    };
+
+    resource function post path_with_request_body(@http:Payload string payload) returns http:NotFound? {
+    };
+}
diff --git a/openapi-cli/src/test/resources/testng.xml b/openapi-cli/src/test/resources/testng.xml
index 8c4eaeafb..48633fc0b 100644
--- a/openapi-cli/src/test/resources/testng.xml
+++ b/openapi-cli/src/test/resources/testng.xml
@@ -104,6 +104,7 @@ under the License.
             <class name="io.ballerina.openapi.generators.testcases.BallerinaTestGeneratorTests"/>
             <class name="io.ballerina.openapi.generators.client.OneOfResponsesTests"/>
             <class name="io.ballerina.openapi.generators.openapi.DataTypeTests"/>
+            <class name="io.ballerina.openapi.generators.openapi.NegativeResponseTests"/>
             <!--            <class name="io.ballerina.openapi.generators.schema.SwaggerParserTests"/>-->
         </classes>
     </test>