code: protected <T> Optional<T> executeGetRequest(URI uri, GenericType<T> returnType)
      {
          return executeGetRequest(uri, null, null, returnType);
      }
docs: Execute a GET request and return the result.
  @param <T> The type parameter used for the return object
  @param uri The URI to call
  @param returnType The type to marshall the result back into
  @return The return type