@Override
    public CodeBlock toProxy(CodeBlock expression) {
      return expression;
    }
Set if this factory should return a serializer that is considered an identity serializer.

<p>The underlying fake serializer implementation will always be an identity serializer. This
only changes the {@link Serializer#isIdentity} return value.
value/src/test/java/com/google/auto/value/extension/serializable/serializer/utils/FakeSerializerFactory.java