Error Evaluating the core model from rasa core

Hi all, I am trying to evaluate a rasa model that I generate using rasa train core I use the rasa version 1.2.1 on Ubuntu 16.04.

Here is the code that I have use:

rasa test core --stories train_test_split/ --out train_test_split

Processed Story Blocks: 0it [00:00, ?it/s]
2019-08-08 22:00:17 WARNING  - There is no starting story block in the training data. All your story blocks start with some checkpoint. There should be at least one story block that starts without any checkpoint.
2019-08-08 22:00:17 INFO     rasa.core.test  - Evaluating 0 stories
0it [00:00, ?it/s]
2019-08-08 22:00:17 INFO     rasa.core.test  - Finished collecting predictions.
Traceback (most recent call last):
  File "$HOME/paysikabot/bin/rasa", line 10, in <module>
  File "$HOME/paysikabot/lib/python3.7/site-packages/rasa/", line 76, in main
  File "$HOME/paysikabot/lib/python3.7/site-packages/rasa/cli/", line 89, in test_core
  File "$HOME/paysikabot/lib/python3.7/site-packages/rasa/", line 108, in test_core
    rasa.core.test(stories, _agent, out_directory=output, **kwargs)
  File "uvloop/loop.pyx", line 1451, in uvloop.loop.Loop.run_until_complete
  File "$HOME/paysikabot/lib/python3.7/site-packages/rasa/core/", line 487, in test
    completed_trackers, agent, fail_on_prediction_errors, e2e
  File "$HOME/paysikabot/lib/python3.7/site-packages/rasa/core/", line 431, in collect_story_predictions
    [1] * len(completed_trackers), correct_dialogues
  File "$HOME/paysikabot/lib/python3.7/site-packages/rasa/nlu/", line 159, in get_evaluation_metrics
    targets, predictions, output_dict=output_dict
  File "$HOME/paysikabot/lib/python3.7/site-packages/sklearn/metrics/", line 1568, in classification_report
    name_width = max(len(cn) for cn in target_names)
ValueError: max() arg is an empty sequence```

Please share your story files.