Error: Module for policy 'EntitySynonymMapper' could not be loaded.

[Krogsager]

Rasa version: 1.4.5

Rasa X version (if used & relevant): 0.22.2

Python version: 3.7.5 AND 3.6.9

Operating system (windows, osx, ...): Ubuntu 18.04.3 LTS

Issue:
I've added EntitySynonymMapper to my config.yml in the RasaX UI. When I click Train, I get an error message.
I've tested this in a fresh docker container in both python 36 and 37.

Error when I press Train in UI:
Error (including full traceback):

Training Core model...
2019-11-22 09:49:57 ERROR    rasax.community.api.blueprints.models  - 500, Internal Server Error, body='b'{"version":"1.4.5","status":"failure","message":"An unexpected error occurred during training. 
Error: Module for policy \'EntitySynonymMapper\' could not be loaded. Please make sure the name is a valid policy.","reason":"TrainingError","details":{},"help":null,"code":500}''    

Error when I train from the command line:
Command or request that led to error:

rasa train

Error (including full traceback):

2019-11-22 09:57:39 INFO     rasa.model  - Data (core-config) for Core model changed.
�[94mTraining Core model...�[0m
2019-11-22 09:57:44 INFO     absl  - Entry Point [tensor2tensor.envs.tic_tac_toe_env:TicTacToeEnv] registered with id [T2TEnv-TicTacToeEnv-v0]
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/rasa/core/policies/ensemble.py", line 319, in from_dict
    constr_func = registry.policy_from_module_path(policy_name)
  File "/usr/local/lib/python3.6/site-packages/rasa/core/registry.py", line 21, in policy_from_module_path
    module_path, lookup_path="rasa.core.policies.registry"
  File "/usr/local/lib/python3.6/site-packages/rasa/utils/common.py", line 191, in class_from_module_path
    return getattr(m, module_path)
AttributeError: module 'rasa.core.policies.registry' has no attribute 'EntitySynonymMapper'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/bin/rasa", line 8, in <module>
    sys.exit(main())
  File "/usr/local/lib/python3.6/site-packages/rasa/__main__.py", line 76, in main
    cmdline_arguments.func(cmdline_arguments)
  File "/usr/local/lib/python3.6/site-packages/rasa/cli/train.py", line 76, in train
    kwargs=extract_additional_arguments(args),
  File "/usr/local/lib/python3.6/site-packages/rasa/train.py", line 45, in train
    kwargs=kwargs,
  File "uvloop/loop.pyx", line 1456, in uvloop.loop.Loop.run_until_complete
  File "/usr/local/lib/python3.6/site-packages/rasa/train.py", line 96, in train_async
    kwargs,
  File "/usr/local/lib/python3.6/site-packages/rasa/train.py", line 182, in _train_async_internal
    kwargs=kwargs,
  File "/usr/local/lib/python3.6/site-packages/rasa/train.py", line 217, in _do_training
    kwargs=kwargs,
  File "/usr/local/lib/python3.6/site-packages/rasa/train.py", line 346, in _train_core_with_validated_data
    kwargs=kwargs,
  File "/usr/local/lib/python3.6/site-packages/rasa/core/train.py", line 43, in train
    policies = config.load(policy_config)
  File "/usr/local/lib/python3.6/site-packages/rasa/core/config.py", line 28, in load
    return PolicyEnsemble.from_dict(config_data)
  File "/usr/local/lib/python3.6/site-packages/rasa/core/policies/ensemble.py", line 327, in from_dict
    "".format(policy_name)
rasa.core.policies.ensemble.InvalidPolicyConfig: Module for policy 'EntitySynonymMapper' could not be loaded. Please make sure the name is a valid policy.

Content of configuration file (config.yml) (if relevant):

language: en
pipeline: supervised_embeddings
policies:
  - name: MemoizationPolicy
  - name: KerasPolicy
  - name: MappingPolicy
  - name: EntitySynonymMapper

The Dockerfile I used:
(only change the first line, FROM python:3.7-stretch to FROM python:3.6-stretch)

FROM python:3.7-stretch
ENV PYTHONDONTWRITEBYTECODE 1
ENV PYTHONUNBUFFERED 1

RUN pip install --upgrade pip
RUN pip install rasa-x --extra-index-url https://pypi.rasa.com/simple

RUN useradd --create-home appuser
WORKDIR /home/appuser
USER appuser

RUN rasa init --no-prompt
CMD ["rasa","x","--no-prompt","--log-file","log"]

[erohmensing]

@Krogsager EntitySynonymMapper is part of the NLU pipeline, not a policy. It is actually already part of the supervised_embeddings pipeline, so you don't need to add it. Simply remove it from the policies list and it should work.