Merge pull request #4989 from RasaHQ/empty-domain-for-nlu-models

use empty domain in case Domain is None (e.g. if it's a NLU only model)

changelog/4989.bugfix.rst

@@ -0,0 +1,2 @@
+Use an empty domain in case a model is loaded which has no domain
+(avoids errors when accessing ``agent.doman.<some attribute>``).

rasa/core/agent.py

@@ -336,7 +336,7 @@ def update_model(
         interpreter: Optional[NaturalLanguageInterpreter] = None,
         model_directory: Optional[Text] = None,
     ) -> None:
-        self.domain = domain
+        self.domain = self._create_domain(domain)
         self.policy_ensemble = policy_ensemble
 
         if interpreter:
@@ -858,7 +858,7 @@ def create_processor(
         )
 
     @staticmethod
-    def _create_domain(domain: Union[Domain, Text]) -> Domain:
+    def _create_domain(domain: Union[Domain, Text, None]) -> Domain:
 
         if isinstance(domain, str):
             domain = Domain.load(domain)

tests/core/test_agent.py

@@ -250,13 +250,10 @@ def test_two_stage_fallback_without_deny_suggestion(domain, policy_config):
 async def test_agent_update_model_none_domain(trained_model: Text):
     agent = await load_agent(model_path=trained_model)
     agent.update_model(
-        Domain.empty(),
-        None,
-        agent.fingerprint,
-        agent.interpreter,
-        agent.model_directory,
+        None, None, agent.fingerprint, agent.interpreter, agent.model_directory
     )
 
+    assert agent.domain is not None
     sender_id = "test_sender_id"
     message = UserMessage("hello", sender_id=sender_id)
     await agent.handle_message(message)