# Buggy code
def guess_format(filename: Text) -> Text:
    """Applies heuristics to guess the data format of a file.

    Args:
        filename: file whose type should be guessed

    Returns:
        Guessed file format.
    """
    guess = UNK
    content = rasa.utils.io.read_file(filename)
    try:
        js = json.loads(content)
    except ValueError:
        if any([marker in content for marker in _markdown_section_markers]):
            guess = MARKDOWN
    else:
        for fformat, format_heuristic in _json_format_heuristics.items():
            if format_heuristic(js, filename):
                guess = fformat
                break

    return guess


# Traceback (FileNotFoundError)
? Export stories to (if file exists, this will append the stories)
? Export NLU data to (if file exists, this will merge learned data with previous training examples)
? Export domain file to (if file exists, this will be overwritten) domain.yml
2019-06-18 08:16:35 ERROR    rasa.core.training.interactive  - An exception occurred while recording messages.
Traceback (most recent call last):
File "/Users/erohmensing/rasa/rasa/core/training/interactive.py", line 1367, in record_messages
endpoint, sender_id, sender_ids, plot_file
File "/Users/erohmensing/rasa/rasa/core/training/interactive.py", line 885, in _predict_till_next_listen
action_name, policy, confidence, predictions, endpoint, sender_id
File "/Users/erohmensing/rasa/rasa/core/training/interactive.py", line 1024, in _validate_action
is_correct = await _ask_questions(question, sender_id, endpoint)
File "/Users/erohmensing/rasa/rasa/core/training/interactive.py", line 312, in _ask_questions
should_retry = await _ask_if_quit(sender_id, endpoint)
File "/Users/erohmensing/rasa/rasa/core/training/interactive.py", line 591, in _ask_if_quit
await _write_data_to_file(sender_id, endpoint)
File "/Users/erohmensing/rasa/rasa/core/training/interactive.py", line 566, in _write_data_to_file
await _write_stories_to_file(story_path, events)
File "/Users/erohmensing/rasa/rasa/core/training/interactive.py", line 764, in _write_stories_to_file
with open(export_story_path, append_write, encoding="utf-8") as f:
FileNotFoundError: [Errno 2] No such file or directory: ''
2019-06-18 08:16:35 ERROR    asyncio  - Task exception was never retrieved
future: <Task finished coro=<_serve_application.<locals>.run_interactive_io() done, defined at /Users/erohmensing/rasa/rasa/core/training/interactive.py:1409> exception=FileNotFoundError(2, 'No such file or directory')>
Traceback (most recent call last):
File "/Users/erohmensing/rasa/rasa/core/training/interactive.py", line 1416, in run_interactive_io
sender_id=uuid.uuid4().hex,
File "/Users/erohmensing/rasa/rasa/core/training/interactive.py", line 1367, in record_messages
endpoint, sender_id, sender_ids, plot_file
File "/Users/erohmensing/rasa/rasa/core/training/interactive.py", line 885, in _predict_till_next_listen
action_name, policy, confidence, predictions, endpoint, sender_id
File "/Users/erohmensing/rasa/rasa/core/training/interactive.py", line 1024, in _validate_action
is_correct = await _ask_questions(question, sender_id, endpoint)
File "/Users/erohmensing/rasa/rasa/core/training/interactive.py", line 312, in _ask_questions
should_retry = await _ask_if_quit(sender_id, endpoint)
File "/Users/erohmensing/rasa/rasa/core/training/interactive.py", line 591, in _ask_if_quit
await _write_data_to_file(sender_id, endpoint)
File "/Users/erohmensing/rasa/rasa/core/training/interactive.py", line 566, in _write_data_to_file
await _write_stories_to_file(story_path, events)
File "/Users/erohmensing/rasa/rasa/core/training/interactive.py", line 764, in _write_stories_to_file
with open(export_story_path, append_write, encoding="utf-8") as f:
FileNotFoundError: [Errno 2] No such file or directory: ''

# Fixed code
def guess_format(filename: Text) -> Text:
    """Applies heuristics to guess the data format of a file.

    Args:
        filename: file whose type should be guessed

    Returns:
        Guessed file format.
    """
    guess = UNK

    content = ""
    try:
        content = rasa.utils.io.read_file(filename)
        js = json.loads(content)
    except ValueError:
        if any([marker in content for marker in _markdown_section_markers]):
            guess = MARKDOWN
    else:
        for fformat, format_heuristic in _json_format_heuristics.items():
            if format_heuristic(js, filename):
                guess = fformat
                break

    return guess