@Override
    public TypeMirror proxyFieldType() {
      TypeElement immutableListTypeElement =
          processingEnv.getElementUtils().getTypeElement(ImmutableList.class.getCanonicalName());
      TypeMirror containedProxyType = containedTypeSerializer.proxyFieldType();
      return processingEnv
          .getTypeUtils()
          .getDeclaredType(immutableListTypeElement, containedProxyType);
    }
A {@link SerializerExtension} that deserializes objects inside an {@link ImmutableList}.

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