refs #3345 - fixes logic and tests

Author: frantuma

modules/swagger-core/src/main/java/io/swagger/v3/core/filter/SpecFilter.java

@@ -291,11 +291,10 @@ private void addSchemaRef(Schema schema, Set<String> referencedDefinitions) {
             referencedDefinitions.add(schema.get$ref());
             return;
         }
-        if (schema.getDiscriminator() != null) {
+        if (schema.getDiscriminator() != null && schema.getDiscriminator().getMapping() != null) {
             for (Map.Entry<String, String> mapping: schema.getDiscriminator().getMapping().entrySet()) {
                 referencedDefinitions.add(mapping.getValue());
             }
-            return;
         }
 
         if (schema.getProperties() != null) {

modules/swagger-core/src/test/java/io/swagger/v3/core/filter/SpecFilterTest.java

@@ -268,6 +268,8 @@ public void shouldRemoveBrokenNestedRefs() throws IOException {
         assertNotNull(filtered.getComponents().getSchemas().get("oneOfNestedParentB"));
         assertNotNull(filtered.getComponents().getSchemas().get("discriminatorParent"));
         assertNotNull(filtered.getComponents().getSchemas().get("discriminatorMatchedChildA"));
+        assertNotNull(filtered.getComponents().getSchemas().get("discriminatorRefProperty"));
+        assertNotNull(filtered.getComponents().getSchemas().get("discriminatorParentRefProperty"));
         assertNotNull(filtered.getComponents().getSchemas().get("discriminatorMatchedChildB"));
     }
 

modules/swagger-core/src/test/resources/specFiles/petstore-3.0-v2-ticket-3303.json

@@ -404,6 +404,18 @@
         }
       },
       "discriminatorMatchedChildA": {
+        "type": "object",
+        "properties": {
+          "parentBStuff": {
+            "type": "integer",
+            "format": "int64"
+          },
+          "discriminatorRefProperty": {
+            "$ref": "#/components/schemas/discriminatorRefProperty"
+          }
+        }
+      },
+      "discriminatorRefProperty": {
         "type": "object",
         "properties": {
           "parentBStuff": {
@@ -421,12 +433,24 @@
           }
         }
       },
+      "discriminatorParentRefProperty": {
+        "type": "object",
+        "properties": {
+          "parentBStuff": {
+            "type": "integer",
+            "format": "int64"
+          }
+        }
+      },
       "discriminatorParent": {
         "type": "object",
         "properties": {
           "parentBStuff": {
             "type": "integer",
             "format": "int64"
+          },
+          "discriminatorParentRefProperty": {
+            "$ref": "#/components/schemas/discriminatorParentRefProperty"
           }
         },
         "discriminator": {