// Note(bmzhao): canonicalized_input_signature should be a tuple of
  // (args, kwargs), where args is an empty tuple, and kwargs is a dictionary of
  // string keys to TensorSpecs.
  if (!canonicalized_input_signature.has_tuple_value()) {
    return absl::FailedPreconditionError(absl::StrCat(
        "SignatureDefFunction's canonicalized_input_signature should be "
        "of form tuple(tuple(), dict()), but was instead: \n",