fix keyerror introduced by #3985

openslides/users/apps.py

@@ -13,6 +13,7 @@ class UsersAppConfig(AppConfig):
 
     def ready(self):
         # Import all required stuff.
+        from . import serializers  # noqa
         from ..core.signals import post_permission_creation, permission_change
         from ..utils.rest_api import router
         from .projector import get_projector_elements

openslides/utils/models.py

@@ -135,5 +135,13 @@ class RESTModelMixin:
         """
         Returns the full_data of the instance.
         """
+        try:
+            serializer_class = model_serializer_classes[type(self)]
+        except KeyError:
+            # Because of the order of imports, it can happen, that the serializer
+            # for a model is not imported yet. Try to guess the name of the
+            # module and import it.
+            module_name = type(self).__module__.rsplit(".", 1)[0] + ".serializers"
+            __import__(module_name)
             serializer_class = model_serializer_classes[type(self)]
         return serializer_class(self).data