Expose newJsonWriter wrapper instead of just options.

This is more future proof to ensure that consumers holding on to TypeAdapters for efficiency can always encode JSON in the same way as if the Gson instance was used directly.

gson/src/main/java/com/google/gson/Gson.java

@@ -247,11 +247,6 @@ public Gson() {
     this.factories = Collections.unmodifiableList(factories);
   }
 
-  /** Returns true if this Gson instance writes fields with null values. */
-  public boolean serializeNulls() {
-    return serializeNulls;
-  }
-
   private TypeAdapter<Number> doubleAdapter(boolean serializeSpecialFloatingPointValues) {
     if (serializeSpecialFloatingPointValues) {
       return TypeAdapters.DOUBLE;
@@ -648,10 +643,9 @@ public void toJson(JsonElement jsonElement, Appendable writer) throws JsonIOExce
   }
 
   /**
-   * Returns a new JSON writer configured for this GSON and with the non-execute
-   * prefix if that is configured.
+   * Returns a new JSON writer configured for the settings on this Gson instance.
    */
-  private JsonWriter newJsonWriter(Writer writer) throws IOException {
+  public JsonWriter newJsonWriter(Writer writer) throws IOException {
     if (generateNonExecutableJson) {
       writer.write(JSON_NON_EXECUTABLE_PREFIX);
     }