message: training/checkpoint_management.py - give parameter default value instead of None.
  checkpoint_name="ckpt"
diff: @@ -494,7 +494,7 @@ class CheckpointManager(object):
  """
  def __init__(self, checkpoint, directory,
  - max_to_keep, keep_checkpoint_every_n_hours=None, checkpoint_name=None):
  + max_to_keep, keep_checkpoint_every_n_hours=None, checkpoint_name="ckpt"):
  """Configure a `CheckpointManager` for use in `directory`.
  If a `CheckpointManager` was previously used in `directory`, its
  @@ -547,7 +547,7 @@ class CheckpointManager(object):
  self._max_to_keep = max_to_keep
  self._keep_checkpoint_every_n_hours = keep_checkpoint_every_n_hours
  self._directory = directory
  - self._checkpoint_prefix = os.path.join(directory, checkpoint_name or "ckpt")
  + self._checkpoint_prefix = os.path.join(directory, checkpoint_name)
  recovered_state = get_checkpoint_state(directory)
  current_clock = time.time()
  self._maybe_delete = collections.OrderedDict()
  