Only include nulls in serialization when processing API responses

pom.xml

@@ -246,8 +246,8 @@
                 <artifactId>maven-compiler-plugin</artifactId>
                 <version>${compiler-plugin-version}</version>
                 <configuration>
-                    <source>1.8</source>
-                    <target>1.8</target>
+                    <source>1.7</source>
+                    <target>1.7</target>
                 </configuration>
             </plugin>
             <plugin>

src/main/java/com/ibm/cloud/sdk/core/http/RequestBuilder.java

@@ -12,6 +12,7 @@
  */
 package com.ibm.cloud.sdk.core.http;
 
+import com.google.gson.Gson;
 import com.google.gson.JsonObject;
 import com.ibm.cloud.sdk.core.service.BaseService;
 import com.ibm.cloud.sdk.core.util.GsonSingleton;
@@ -333,12 +334,11 @@ public RequestBuilder bodyContent(InputStream stream, String contentType) {
   public RequestBuilder bodyContent(String contentType, Object jsonContent, Object jsonPatchContent,
     InputStream nonJsonContent) {
     if (contentType != null) {
+      Gson requestGson = GsonSingleton.getGson().newBuilder().serializeNulls().create();
       if (BaseService.isJsonMimeType(contentType)) {
-        this.bodyContent(
-          GsonSingleton.getGson().toJsonTree(jsonContent).getAsJsonObject().toString(), contentType);
+        this.bodyContent(requestGson.toJsonTree(jsonContent).getAsJsonObject().toString(), contentType);
       } else if (BaseService.isJsonPatchMimeType(contentType)) {
-        this.bodyContent(
-          GsonSingleton.getGson().toJsonTree(jsonPatchContent).getAsJsonObject().toString(), contentType);
+        this.bodyContent(requestGson.toJsonTree(jsonPatchContent).getAsJsonObject().toString(), contentType);
       } else {
         this.bodyContent(nonJsonContent, contentType);
       }

src/main/java/com/ibm/cloud/sdk/core/http/ServiceCall.java

@@ -44,7 +44,7 @@ public interface ServiceCall<T> {
    *
    * @param callback the callback
    */
-  void enqueue(ServiceCallback<? super T> callback);
+  void enqueue(ServiceCallback<T> callback);
 
   /**
    * Reactive request using the RxJava 2 library. See https://github.com/ReactiveX/RxJava. In addition, the wrapped

src/main/java/com/ibm/cloud/sdk/core/service/BaseService.java

@@ -490,7 +490,7 @@ public com.ibm.cloud.sdk.core.http.Response<T> execute() {
     }
 
     @Override
-    public void enqueue(final ServiceCallback<? super T> callback) {
+    public void enqueue(final ServiceCallback<T> callback) {
       call.enqueue(new Callback() {
         @Override
         public void onFailure(Call call, IOException e) {

src/main/java/com/ibm/cloud/sdk/core/service/security/IamTokenManager.java

@@ -182,7 +182,7 @@ private boolean isRefreshTokenExpired() {
    * @param request the request for the IAM API
    * @return object containing requested IAM token information
    */
-  private IamToken callIamApi(Request request) {
+  private IamToken callIamApi(final Request request) {
     final IamToken[] returnToken = new IamToken[1];
 
     Thread iamApiCall = new Thread(new Runnable() {

src/main/java/com/ibm/cloud/sdk/core/util/GsonSingleton.java

@@ -45,7 +45,6 @@ private static Gson createGson(Boolean prettyPrint) {
       builder.setPrettyPrinting();
     }
     builder.disableHtmlEscaping();
-    builder.serializeNulls();
     return builder.create();
   }