message: Don't throw errors if non-Checkpointable objects are passed to MultiRNNCell
diff: @@ -46,6 +46,7 @@ from tensorflow.python.ops import tensor_array_ops
  from tensorflow.python.ops import variable_scope as vs
  from tensorflow.python.ops import variables as tf_variables
  from tensorflow.python.platform import tf_logging as logging
  +from tensorflow.python.training import checkpointable
  from tensorflow.python.util import nest
  from tensorflow.python.util.tf_export import tf_export
  @@ -1190,6 +1191,8 @@ class MultiRNNCell(RNNCell):
  for cell_number, cell in enumerate(self._cells):
  # Add Checkpointable dependencies on these cells so their variables get
  # saved with this object when using object-based saving.
  + if isinstance(cell, checkpointable.CheckpointableBase):
  + # TODO(allenl): Track down non-Checkpointable callers.
  self._track_checkpointable(cell, name="cell-%d" % (cell_number,))
  self._state_is_tuple = state_is_tuple
  if not state_is_tuple:
  