Handle Null Cases

Previously, a change went in that created or updated applications with
environment variables from a manifest.  This change did not handle null cases
properly.  This change updates the code to handle that case.

Author: nebhale

cloudfoundry-operations/src/main/java/org/cloudfoundry/operations/applications/DefaultApplications.java

@@ -709,7 +709,7 @@ private static Mono<String> getApplicationId(CloudFoundryClient cloudFoundryClie
             .singleOrEmpty()
             .then(application -> {
                 Map<String, Object> environmentJsons = new HashMap<>(ResourceUtils.getEntity(application).getEnvironmentJsons());
-                environmentJsons.putAll(manifest.getEnvironmentVariables());
+                Optional.ofNullable(manifest.getEnvironmentVariables()).ifPresent(environmentJsons::putAll);
 
                 return requestUpdateApplication(cloudFoundryClient, ResourceUtils.getId(application), environmentJsons, manifest, stackId)
                     .map(ResourceUtils::getId);

cloudfoundry-operations/src/test/java/org/cloudfoundry/operations/applications/DefaultApplicationsTest.java

@@ -1170,6 +1170,7 @@ public void pushExistingApplication() throws IOException {
         requestApplications(this.cloudFoundryClient, "test-name", TEST_SPACE_ID, "test-application-id");
         requestUpdateApplication(this.cloudFoundryClient, "test-application-id", ApplicationManifest.builder()
             .path(testApplication)
+            .environmentVariable("test-var", "test-value")
             .domain("test-shared-domain")
             .name("test-name")
             .build(), null);