Catch some tracebacks

server/openslides/motions/views.py

@@ -6,6 +6,7 @@ from django.contrib.auth import get_user_model
 from django.db import transaction
 from django.db.models import Case, When
 from django.db.models.deletion import ProtectedError
+from django.db.utils import IntegrityError
 from django.http.request import QueryDict
 from rest_framework import status
 
@@ -514,7 +515,10 @@ class MotionViewSet(TreeSortMixin, ModelViewSet):
                 and not motion.is_supporter(request.user)
             ):
                 raise ValidationError({"detail": "You can not support this motion."})
+            try:
                 motion.supporters.add(request.user)
+            except IntegrityError:
+                raise ValidationError({"detail": "You are already a supporter."})
             # Send new supporter via autoupdate because users without permission
             # to see users may not have it but can get it now.
             # TODO: Skip history.

server/openslides/utils/models.py

@@ -6,6 +6,7 @@ from django.db import models
 
 from . import logging
 from .access_permissions import BaseAccessPermissions
+from .auth import UserDoesNotExist
 from .autoupdate import AutoupdateElement, inform_changed_data, inform_elements
 from .rest_api import model_serializer_classes
 from .utils import convert_camel_case_to_pseudo_snake_case, get_element_id
@@ -185,7 +186,12 @@ class RESTModelMixin:
         """
         Converts a list of elements from full_data to restricted_data.
         """
-        return await cls.get_access_permissions().get_restricted_data(elements, user_id)
+        try:
+            return await cls.get_access_permissions().get_restricted_data(
+                elements, user_id
+            )
+        except UserDoesNotExist:
+            return []
 
     def get_full_data(self) -> Dict[str, Any]:
         """