message: Add a default value of None for the newly added parameter.
diff: @@ -152,7 +152,7 @@ class StopAfterNTrees(session_run_hook.SessionRunHook):
  """Stop training after building N full trees."""
  def __init__(self, n, num_attempted_trees_tensor, num_finalized_trees_tensor,
  - override_global_step_value):
  + override_global_step_value=None):
  self._num_trees = n
  # num_attempted_trees_tensor and num_finalized_trees_tensor are both
  # tensors.
  