# Buggy code
def train(
    self,
    training_data: TrainingData,
    config: Optional[RasaNLUModelConfig] = None,
    **kwargs: Any,
) -> None:
    # checks whether there is at least one
    # example with an entity annotation
    if not training_data.entity_examples:
        logger.debug(
            "No training examples with entities present. Skip training"
            "of 'CRFEntityExtractor'."
        )
        return

    self.check_correct_entity_annotations(training_data)

    if self.component_config[BILOU_FLAG]:
        bilou_utils.apply_bilou_schema(training_data)

    # only keep the CRFs for tags we actually have training data for
    self._update_crf_order(training_data)

    # filter out pre-trained entity examples
    entity_examples = self.filter_trainable_entities(training_data.training_examples)

    dataset = [self._convert_to_crf_tokens(example) for example in entity_examples]

    self._train_model(dataset)


# Traceback (sklearn.exceptions.NotFittedError)
(rasa) ➜  ~/Repositories/rasa/demo_bot git:(core-entity-roles-groups) ✔ rasa train
The configuration for policies was chosen automatically. It was written into the config file at 'config.yml'.
Training NLU model...
2020-10-06 09:34:09 INFO     rasa.shared.nlu.training_data.training_data  - Training data stats:
2020-10-06 09:34:09 INFO     rasa.shared.nlu.training_data.training_data  - Number of intent examples: 69 (7 distinct intents)

2020-10-06 09:34:09 INFO     rasa.shared.nlu.training_data.training_data  -   Found intents: 'deny', 'mood_great', 'mood_unhappy', 'affirm', 'greet', 'bot_challenge', 'goodbye'
2020-10-06 09:34:09 INFO     rasa.shared.nlu.training_data.training_data  - Number of response examples: 0 (6 distinct responses)
2020-10-06 09:34:09 INFO     rasa.shared.nlu.training_data.training_data  - Number of entity examples: 0 (0 distinct entities)
2020-10-06 09:34:09 INFO     rasa.nlu.model  - Starting to train component WhitespaceTokenizer
2020-10-06 09:34:09 INFO     rasa.nlu.model  - Finished training component.
2020-10-06 09:34:09 INFO     rasa.nlu.model  - Starting to train component RegexEntityExtractor
/home/tanja/Repositories/rasa/rasa/shared/utils/io.py:88: UserWarning: No lookup tables or regexes defined in the training data that have a name equal to any entity in the training data. In order for this component to work you need to define valid lookup tables or regexes in the training data.
2020-10-06 09:34:09 INFO     rasa.nlu.model  - Finished training component.
2020-10-06 09:34:09 INFO     rasa.nlu.model  - Starting to train component LexicalSyntacticFeaturizer
2020-10-06 09:34:09 INFO     rasa.nlu.model  - Finished training component.
2020-10-06 09:34:09 INFO     rasa.nlu.model  - Starting to train component CountVectorsFeaturizer
2020-10-06 09:34:09 INFO     rasa.nlu.model  - Finished training component.
2020-10-06 09:34:09 INFO     rasa.nlu.model  - Starting to train component CountVectorsFeaturizer
/home/tanja/.virtualenv/rasa/lib/python3.6/site-packages/sklearn/feature_extraction/text.py:501: UserWarning: The parameter 'token_pattern' will not be used since 'analyzer' != 'word'
warnings.warn("The parameter 'token_pattern' will not be used"
2020-10-06 09:34:09 INFO     rasa.nlu.model  - Finished training component.
2020-10-06 09:34:09 INFO     rasa.nlu.model  - Starting to train component DIETClassifier
/home/tanja/Repositories/rasa/rasa/shared/utils/io.py:88: UserWarning: You specified 'DIET' to train entities, but no entities are present in the training data. Skip training of entities.
Epochs: 100%|█████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 100/100 [00:18<00:00,  5.46it/s, t_loss=1.504, i_acc=0.986]
2020-10-06 09:34:36 INFO     rasa.utils.tensorflow.models  - Finished training.
2020-10-06 09:34:36 INFO     rasa.nlu.model  - Finished training component.
2020-10-06 09:34:36 INFO     rasa.nlu.model  - Starting to train component EntitySynonymMapper
2020-10-06 09:34:36 INFO     rasa.nlu.model  - Finished training component.
2020-10-06 09:34:36 INFO     rasa.nlu.model  - Starting to train component ResponseSelector
2020-10-06 09:34:36 INFO     rasa.nlu.selectors.response_selector  - Retrieval intent parameter was left to its default value. This response selector will be trained on training examples combining all retrieval intents.
2020-10-06 09:34:36 INFO     rasa.nlu.model  - Finished training component.
2020-10-06 09:34:36 INFO     rasa.nlu.model  - Starting to train component FallbackClassifier
2020-10-06 09:34:36 INFO     rasa.nlu.model  - Finished training component.
2020-10-06 09:34:36 INFO     rasa.nlu.model  - Successfully saved model into '/tmp/tmp1hnllvoo/nlu'
NLU model training completed.
Training Core model...
Processed story blocks: 100%|████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 3/3 [00:00<00:00, 2265.97it/s, # trackers=1]
Processed story blocks: 100%|█████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 3/3 [00:00<00:00, 798.51it/s, # trackers=3]
Processed story blocks: 100%|████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 3/3 [00:00<00:00, 269.55it/s, # trackers=12]
Processed story blocks: 100%|█████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 3/3 [00:00<00:00, 83.32it/s, # trackers=39]
Processed rules: 100%|███████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 2/2 [00:00<00:00, 2965.22it/s, # trackers=1]
Processed trackers: 100%|█████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 3/3 [00:00<00:00, 911.94it/s, # actions=12]
Processed actions: 12it [00:00, 9763.66it/s, # examples=12]
Processed trackers: 100%|█████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 120/120 [00:00<00:00, 230.98it/s, # actions=30]
Traceback (most recent call last):
File "/home/tanja/.virtualenv/rasa/bin/rasa", line 11, in <module>
load_entry_point('rasa', 'console_scripts', 'rasa')()
File "/home/tanja/Repositories/rasa/rasa/__main__.py", line 116, in main
cmdline_arguments.func(cmdline_arguments)
File "/home/tanja/Repositories/rasa/rasa/cli/train.py", line 90, in train
nlu_additional_arguments=extract_nlu_additional_arguments(args),
File "/home/tanja/Repositories/rasa/rasa/train.py", line 55, in train
loop,
File "/home/tanja/Repositories/rasa/rasa/utils/common.py", line 300, in run_in_loop
result = loop.run_until_complete(f)
File "uvloop/loop.pyx", line 1456, in uvloop.loop.Loop.run_until_complete
File "/home/tanja/Repositories/rasa/rasa/train.py", line 110, in train_async
nlu_additional_arguments=nlu_additional_arguments,
File "/home/tanja/Repositories/rasa/rasa/train.py", line 207, in _train_async_internal
old_model_zip_path=old_model,
File "/home/tanja/Repositories/rasa/rasa/train.py", line 263, in _do_training
or _interpreter_from_previous_model(old_model_zip_path),
File "/home/tanja/Repositories/rasa/rasa/train.py", line 409, in _train_core_with_validated_data
interpreter=interpreter,
File "/home/tanja/Repositories/rasa/rasa/core/train.py", line 67, in train
agent.train(training_data, **additional_arguments)
File "/home/tanja/Repositories/rasa/rasa/core/agent.py", line 724, in train
training_trackers, self.domain, interpreter=self.interpreter, **kwargs
File "/home/tanja/Repositories/rasa/rasa/core/policies/ensemble.py", line 189, in train
trackers_to_train, domain, interpreter=interpreter, **kwargs
File "/home/tanja/Repositories/rasa/rasa/core/policies/ted_policy.py", line 332, in train
training_trackers, domain, interpreter, **kwargs
File "/home/tanja/Repositories/rasa/rasa/core/policies/policy.py", line 165, in featurize_for_training
training_trackers, domain, interpreter
File "/home/tanja/Repositories/rasa/rasa/core/featurizers/tracker_featurizers.py", line 140, in featurize_trackers
tracker_state_features = self._featurize_states(trackers_as_states, interpreter)
File "/home/tanja/Repositories/rasa/rasa/core/featurizers/tracker_featurizers.py", line 73, in _featurize_states
for tracker_states in trackers_as_states
File "/home/tanja/Repositories/rasa/rasa/core/featurizers/tracker_featurizers.py", line 73, in <listcomp>
for tracker_states in trackers_as_states
File "/home/tanja/Repositories/rasa/rasa/core/featurizers/tracker_featurizers.py", line 71, in <listcomp>
for state in tracker_states
File "/home/tanja/Repositories/rasa/rasa/core/featurizers/single_state_featurizer.py", line 201, in encode_state
self._extract_state_features(sub_state, interpreter, sparse=True)
File "/home/tanja/Repositories/rasa/rasa/core/featurizers/single_state_featurizer.py", line 169, in _extract_state_features
parsed_message = interpreter.featurize_message(message)
File "/home/tanja/Repositories/rasa/rasa/core/interpreter.py", line 158, in featurize_message
result = self.interpreter.featurize_message(message)
File "/home/tanja/Repositories/rasa/rasa/nlu/model.py", line 418, in featurize_message
component.process(message, **self.context)
File "/home/tanja/Repositories/rasa/rasa/nlu/featurizers/sparse_featurizer/count_vectors_featurizer.py", line 562, in process
attribute, [message_tokens]
File "/home/tanja/Repositories/rasa/rasa/nlu/featurizers/sparse_featurizer/count_vectors_featurizer.py", line 438, in _create_features
seq_vec = self.vectorizers[attribute].transform(tokens)
File "/home/tanja/.virtualenv/rasa/lib/python3.6/site-packages/sklearn/feature_extraction/text.py", line 1247, in transform
self._check_vocabulary()
File "/home/tanja/.virtualenv/rasa/lib/python3.6/site-packages/sklearn/feature_extraction/text.py", line 467, in _check_vocabulary
raise NotFittedError("Vocabulary not fitted or provided")
sklearn.exceptions.NotFittedError: Vocabulary not fitted or provided

# Fixed code
def train(
    self,
    training_data: TrainingData,
    config: Optional[RasaNLUModelConfig] = None,
    **kwargs: Any,
) -> None:
    # checks whether there is at least one
    # example with an entity annotation
    if not training_data.entity_examples:
        logger.debug(
            "No training examples with entities present. Skip training"
            "of 'CRFEntityExtractor'."
        )
        return

    self.check_correct_entity_annotations(training_data)

    if self.component_config[BILOU_FLAG]:
        bilou_utils.apply_bilou_schema(training_data)

    # only keep the CRFs for tags we actually have training data for
    self._update_crf_order(training_data)

    # filter out pre-trained entity examples
    entity_examples = self.filter_trainable_entities(training_data.nlu_examples)

    dataset = [self._convert_to_crf_tokens(example) for example in entity_examples]

    self._train_model(dataset)