Running local main fails because `UnifiedWorkspaceOutcomeDeterminer.assistant` is `None`

[victorpaleologue]

Trying to run local_main.py fails with the following error:

$ python local_main.py 
Traceback (most recent call last):
  File "local_main.py", line 13, in <module>
    configuration_provider.check_all_action_builders()
  File "/Users/victor.paleologue/Code/Palaio/HTN/contingent-plan-executor/hovor/configuration/json_configuration_provider.py", line 48, in check_all_action_builders
    self._force_build_of_all_action_builders()
  File "/Users/victor.paleologue/Code/Palaio/HTN/contingent-plan-executor/hovor/configuration/json_configuration_provider.py", line 74, in _force_build_of_all_action_builders
    self._create_action_builder(action_name, action_config)
  File "/Users/victor.paleologue/Code/Palaio/HTN/contingent-plan-executor/hovor/configuration/json_configuration_provider.py", line 176, in _create_action_builder
    outcome_group = self._create_outcome_group(action_name, action_config["effect"])
  File "/Users/victor.paleologue/Code/Palaio/HTN/contingent-plan-executor/hovor/configuration/json_configuration_provider.py", line 188, in _create_outcome_group
    outcome_group, determination_info = self._create_outcome_group_with_determination_info(action_name,
  File "/Users/victor.paleologue/Code/Palaio/HTN/contingent-plan-executor/hovor/configuration/json_configuration_provider.py", line 198, in _create_outcome_group_with_determination_info
    outcome_determiner = self._create_outcome_determiner(action_name, effect_config)
  File "/Users/victor.paleologue/Code/Palaio/HTN/contingent-plan-executor/hovor/configuration/json_configuration_provider.py", line 256, in _create_outcome_determiner
    return UnifiedWorkspaceOutcomeDeterminer(action_name, outcome_config["global-outcome-name"], outcome_config[
  File "/Users/victor.paleologue/Code/Palaio/HTN/contingent-plan-executor/hovor/outcome_determiners/unified_workspace_outcome_determiner.py", line 51, in __init__
    response = UnifiedWorkspaceOutcomeDeterminer.assistant.list_workspaces().get_result()
AttributeError: 'NoneType' object has no attribute 'list_workspaces'
(contingent-plan-executor)