code: def zero_state(self, batch_size, dtype=LayersConfig.tf_dtype):
          
          shape = self.shape
          num_features = self.num_features
          # TODO : TypeError: 'NoneType' object is not subscriptable
          zeros = tf.zeros([batch_size, shape[0], shape[1], num_features * 2], dtype=dtype)
          return zeros
docs: Return zero-filled state tensor(s).
          Args:
            batch_size: int, float, or unit Tensor representing the batch size.
          Returns:
            tensor of shape '[batch_size x shape[0] x shape[1] x num_features]
            filled with zeros