fix: explicitly serialize null values found in dynamic properties

Author: padamstx

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

@@ -1,5 +1,5 @@
 /**
- * (C) Copyright IBM Corp. 2019.
+ * (C) Copyright IBM Corp. 2019, 2020.
  * Copyright (C) 2011 Google Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
@@ -67,6 +67,9 @@
  *
  * <p>This class includes code that was adapted from the internal <code>ReflectiveTypeAdapterFactory</code> and
  * <code>MapTypeAdapterFactory</code> classes from Gson.
+ *
+ * <p>This class will explicitly serialize null values found within dynamic (additional) properties, regardless of
+ * the global "serialize nulls" setting in Gson.
  */
 public class DynamicModelTypeAdapterFactory implements TypeAdapterFactory {
   private static final Logger LOGGER = Logger.getLogger(DynamicModelTypeAdapterFactory.class.getName());
@@ -331,9 +334,17 @@ public void write(JsonWriter out, T value) throws IOException {
         }
 
         // Next, serialize each of the map entries.
-        for (String key : ((DynamicModel<?>) value).getPropertyNames()) {
-          out.name(String.valueOf(key));
-          mapValueTypeAdapter.write(out, ((DynamicModel<?>) value).get(key));
+        // When serializing the map entries (i.e. additional/dynamic properties) we want
+        // to explicitly serialize null values regardless of the global Gson "serialize nulls" setting.
+        boolean serializeNulls = out.getSerializeNulls();
+        out.setSerializeNulls(true);
+        try {
+          for (String key : ((DynamicModel<?>) value).getPropertyNames()) {
+            out.name(String.valueOf(key));
+            mapValueTypeAdapter.write(out, ((DynamicModel<?>) value).get(key));
+          }
+        } finally {
+          out.setSerializeNulls(serializeNulls);
         }
       } catch (IllegalAccessException e) {
         throw new AssertionError(e);

src/test/java/com/ibm/cloud/sdk/core/test/model/DynamicModelSerializationTest.java

@@ -1,5 +1,5 @@
 /**
- * (C) Copyright IBM Corp. 2015, 2019.
+ * (C) Copyright IBM Corp. 2015, 2020.
  *
  * Licensed 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
@@ -54,15 +54,18 @@ private <T> T deserialize(String json, Class<T> clazz) {
     return GsonSingleton.getGson().fromJson(json, clazz);
   }
 
-  private <T> void testSerDeser(DynamicModel<?> model, Class<T> clazz) {
-    String jsonString = serialize(model);
+  private void display(String msg) {
     if (displayOutput) {
-      System.out.println("serialized " + model.getClass().getSimpleName() + ": " + jsonString);
+      System.out.println(msg);
     }
+  }
+
+  private <T> void testSerDeser(DynamicModel<?> model, Class<T> clazz) {
+    String jsonString = serialize(model);
+
+    display("serialized " + model.getClass().getSimpleName() + ": " + jsonString);
     T newModel = deserialize(jsonString, clazz);
-    if (displayOutput) {
-      System.out.println("de-serialized " + model.getClass().getSimpleName() + ": " + newModel.toString());
-    }
+    display("de-serialized " + model.getClass().getSimpleName() + ": " + newModel.toString());
     assertEquals(newModel, model);
   }
 
@@ -203,19 +206,31 @@ public void testNoCtor() {
   public void testNullValues() {
     ModelAPFoo model = createModelAPFoo();
     model.setProp1(null);
-    // model.put("basketball", "foo");
     testSerDeser(model, ModelAPFoo.class);
   }
 
+  @Test
+  public void testAddlPropsNull() {
+    ModelAPString model = createModelAPString();
+    model.put("basketball", null);
+
+    String json = serialize(model);
+    display("Serialized: " + json);
+    assertTrue(json.contains("\"basketball\": null"));
+
+    ModelAPString newModel = deserialize(json, ModelAPString.class);
+    assertEquals(newModel, model);
+  }
+
   @Test(expectedExceptions = {JsonSyntaxException.class})
   public void testBadDeser() {
 
     // Obtain the json string and then render it incorrect to trigger a deserialization error.
     ModelAPFoo model = createModelAPFoo();
     String goodJson = serialize(model);
-    if (displayOutput) System.out.println("Serialized ModelAPFoo: " + goodJson);
+    display("Serialized ModelAPFoo: " + goodJson);
     String badJson = goodJson.replaceAll("foo", "FOO").replaceAll("prop2", "var2");
-    if (displayOutput) System.out.println("Incorrect JSON: " + badJson);
+    display("Incorrect JSON: " + badJson);
 
     // We just need to try to deserialize the bad JSON string to trigger the exception.
     deserialize(badJson, ModelAPFoo.class);