@Override
    public TypeMirror proxyFieldType() {
      TypeElement immutableMapTypeElement =
          processingEnv.getElementUtils().getTypeElement(ImmutableMap.class.getCanonicalName());
      return processingEnv
          .getTypeUtils()
          .getDeclaredType(immutableMapTypeElement, keyProxyType, valueProxyType);
    }
A {@link SerializerExtension} that deserializes objects inside an {@link ImmutableMap}.

<p>Enables unserializable objects inside an ImmutableMap to be serializable.
value/src/main/java/com/google/auto/value/extension/serializable/serializer/impl/ImmutableMapSerializerExtension.java