message: Fix checkpoint_path is None handling in export_fn of make_best_model_export_strategy.
diff: @@ -50,6 +50,7 @@ from tensorflow.python.platform import gfile
  from tensorflow.python.platform import tf_logging as logging
  from tensorflow.python.saved_model import signature_constants
  from tensorflow.python.saved_model import signature_def_utils
  +from tensorflow.python.training import saver
  from tensorflow.python.util import compat
  @@ -616,7 +617,13 @@ def make_best_model_export_strategy(serving_input_fn,
  Returns:
  The string path to the exported directory.
  """
  -
  + if not checkpoint_path:
  + # TODO(b/67425018): switch to
  + # checkpoint_path = estimator.latest_checkpoint()
  + # as soon as contrib is cleaned up and we can thus be sure that
  + # estimator is a tf.estimator.Estimator and not a
  + # tf.contrib.learn.Estimator
  + checkpoint_path = saver.latest_checkpoint(estimator.model_dir)
  export_checkpoint_path, export_eval_result = best_model_selector.update(
  checkpoint_path, eval_result)
  