Fixed nullSafe usage.

gson/src/main/java/com/google/gson/internal/bind/JsonAdapterAnnotationTypeAdapterFactory.java

@@ -55,6 +55,7 @@ TypeAdapter<?> getTypeAdapter(ConstructorConstructor constructorConstructor, Gso
     Object instance = constructorConstructor.get(TypeToken.get(annotation.value())).construct();
 
     TypeAdapter<?> typeAdapter;
+    boolean nullSafe = annotation.nullSafe();
     if (instance instanceof TypeAdapter) {
       typeAdapter = (TypeAdapter<?>) instance;
     } else if (instance instanceof TypeAdapterFactory) {
@@ -66,15 +67,16 @@ TypeAdapter<?> getTypeAdapter(ConstructorConstructor constructorConstructor, Gso
       JsonDeserializer<?> deserializer = instance instanceof JsonDeserializer
           ? (JsonDeserializer) instance
           : null;
-      typeAdapter = new TreeTypeAdapter(serializer, deserializer, gson, type, null);
+      typeAdapter = new TreeTypeAdapter(serializer, deserializer, gson, type, null, nullSafe);
+      nullSafe = false;
     } else {
       throw new IllegalArgumentException("Invalid attempt to bind an instance of "
           + instance.getClass().getName() + " as a @JsonAdapter for " + type.toString()
           + ". @JsonAdapter value must be a TypeAdapter, TypeAdapterFactory,"
           + " JsonSerializer or JsonDeserializer.");
     }
 
-    if (typeAdapter != null && annotation.nullSafe()) {
+    if (typeAdapter != null && nullSafe) {
       typeAdapter = typeAdapter.nullSafe();
     }
 

gson/src/main/java/com/google/gson/internal/bind/TreeTypeAdapter.java

@@ -45,25 +45,32 @@ public final class TreeTypeAdapter<T> extends TypeAdapter<T> {
   private final TypeToken<T> typeToken;
   private final TypeAdapterFactory skipPast;
   private final GsonContextImpl context = new GsonContextImpl();
+  private final boolean nullSafe;
 
   /** The delegate is lazily created because it may not be needed, and creating it may fail. */
   private TypeAdapter<T> delegate;
 
   public TreeTypeAdapter(JsonSerializer<T> serializer, JsonDeserializer<T> deserializer,
-      Gson gson, TypeToken<T> typeToken, TypeAdapterFactory skipPast) {
+      Gson gson, TypeToken<T> typeToken, TypeAdapterFactory skipPast, boolean nullSafe) {
     this.serializer = serializer;
     this.deserializer = deserializer;
     this.gson = gson;
     this.typeToken = typeToken;
     this.skipPast = skipPast;
+    this.nullSafe = nullSafe;
+  }
+
+  public TreeTypeAdapter(JsonSerializer<T> serializer, JsonDeserializer<T> deserializer,
+                         Gson gson, TypeToken<T> typeToken, TypeAdapterFactory skipPast) {
+    this(serializer, deserializer, gson, typeToken, skipPast, true);
   }
 
   @Override public T read(JsonReader in) throws IOException {
     if (deserializer == null) {
       return delegate().read(in);
     }
     JsonElement value = Streams.parse(in);
-    if (value.isJsonNull()) {
+    if (nullSafe && value.isJsonNull()) {
       return null;
     }
     return deserializer.deserialize(value, typeToken.getType(), context);
@@ -74,7 +81,7 @@ public TreeTypeAdapter(JsonSerializer<T> serializer, JsonDeserializer<T> deseria
       delegate().write(out, value);
       return;
     }
-    if (value == null) {
+    if (nullSafe && value == null) {
       out.nullValue();
       return;
     }

gson/src/test/java/com/google/gson/functional/JsonAdapterSerializerDeserializerTest.java

@@ -161,4 +161,22 @@ private static final class BaseIntegerAdapter implements JsonSerializer<Base<Int
       return new JsonPrimitive("BaseIntegerAdapter");
     }
   }
+
+  public void testJsonAdapterNullSafe() {
+    Gson gson = new Gson();
+    String json = gson.toJson(new Computer3(null, null));
+    assertEquals("{\"user1\":\"UserSerializerDeserializer\"}", json);
+    Computer3 computer3 = gson.fromJson("{\"user1\":null, \"user2\":null}", Computer3.class);
+    assertEquals("UserSerializerDeserializer", computer3.user1.name);
+    assertNull(computer3.user2);
+  }
+
+  private static final class Computer3 {
+    @JsonAdapter(value = UserSerializerDeserializer.class, nullSafe = false) final User user1;
+    @JsonAdapter(value = UserSerializerDeserializer.class) final User user2;
+    Computer3(User user1, User user2) {
+      this.user1 = user1;
+      this.user2 = user2;
+    }
+  }
 }