Improve typing in Fab

providers/fab/src/airflow/providers/fab/auth_manager/api_endpoints/user_endpoint.py

@@ -120,7 +120,9 @@ def post_user() -> APIResponse:
         raise BadRequest(detail=detail)
 
     if not roles_to_add:  # No roles provided, use the F.A.B's default registered user role.
-        roles_to_add.append(security_manager.find_role(security_manager.auth_user_registration_role))
+        r = security_manager.find_role(security_manager.auth_user_registration_role)
+        if r:
+            roles_to_add.append(r)
 
     user = security_manager.add_user(role=roles_to_add, **data)
     if not user:

providers/fab/src/airflow/providers/fab/auth_manager/fab_auth_manager.py

@@ -272,13 +272,13 @@ def serialize_user(self, user: User) -> dict[str, Any]:
     def is_logged_in(self) -> bool:
         """Return whether the user is logged in."""
         user = self.get_user()
-        return (
+        return bool(
             self.appbuilder
             and self.appbuilder.app.config.get("AUTH_ROLE_PUBLIC", None)
             or (not user.is_anonymous and user.is_active)
         )
 
-    def create_token(self, headers: dict[str, str], body: dict[str, Any]) -> User:
+    def create_token(self, headers: dict[str, str], body: dict[str, Any]) -> User | None:
         """
         Create a new token from a payload.