chore: Don't send no-op RPC calls from serializers

src/sentry/api/serializers/models/activity.py

@@ -17,9 +17,11 @@ def __init__(self, environment_func=None):
     def get_attrs(self, item_list, user, **kwargs):
         # TODO(dcramer); assert on relations
         user_ids = [i.user_id for i in item_list if i.user_id]
-        user_list = user_service.serialize_many(
-            filter={"user_ids": user_ids}, as_user=serialize_generic_user(user)
-        )
+        user_list = []
+        if user_ids:
+            user_list = user_service.serialize_many(
+                filter={"user_ids": user_ids}, as_user=serialize_generic_user(user)
+            )
         users = {u["id"]: u for u in user_list}
 
         commit_ids = {

src/sentry/api/serializers/models/group.py

@@ -183,9 +183,12 @@ def _serialize_assignees(self, item_list: Sequence[Group]) -> Mapping[int, Team
         for team in Team.objects.filter(id__in=all_team_ids.keys()):
             for group_id in all_team_ids[team.id]:
                 result[group_id] = team
-        for user in user_service.get_many_by_id(ids=list(all_user_ids.keys())):
-            for group_id in all_user_ids[user.id]:
-                result[group_id] = user
+
+        user_ids = list(all_user_ids.keys())
+        if user_ids:
+            for user in user_service.get_many_by_id(ids=user_ids):
+                for group_id in all_user_ids[user.id]:
+                    result[group_id] = user
 
         return result
 

src/sentry/api/serializers/models/release.py

@@ -458,13 +458,16 @@ def get_attrs(self, item_list, user, **kwargs):
                 issue_counts_by_release,
             ) = self.__get_release_data_with_environments(release_project_envs)
 
-        owners = {
-            d["id"]: d
-            for d in user_service.serialize_many(
-                filter={"user_ids": [i.owner_id for i in item_list if i.owner_id]},
-                as_user=serialize_generic_user(user),
-            )
-        }
+        owners = {}
+        owner_ids = [i.owner_id for i in item_list if i.owner_id]
+        if owner_ids:
+            owners = {
+                d["id"]: d
+                for d in user_service.serialize_many(
+                    filter={"user_ids": owner_ids},
+                    as_user=serialize_generic_user(user),
+                )
+            }
 
         authors_metadata_attrs = _get_authors_metadata(item_list, user)
         release_metadata_attrs = _get_last_commit_metadata(item_list, user)