user_groups: Do not allow empty group names in backend.

We now raise error if a user tries to create a group with
empty name or tries to update a group name to be empty.

zerver/lib/user_groups.py

@@ -214,6 +214,9 @@ def access_user_group_for_setting(
 
 
 def check_user_group_name(group_name: str) -> str:
+    if group_name.strip() == "":
+        raise JsonableError(_("User group name can't be empty!"))
+
     if len(group_name) > UserGroup.MAX_NAME_LENGTH:
         raise JsonableError(
             _("User group name cannot exceed {max_length} characters.").format(

zerver/tests/test_user_groups.py

@@ -303,6 +303,16 @@ class UserGroupAPITestCase(UserGroupTestCase):
         self.assert_json_error(result, "User group name cannot exceed 100 characters.")
         self.assert_length(UserGroup.objects.filter(realm=hamlet.realm), 10)
 
+        # Test emtpty group name.
+        params = {
+            "name": "",
+            "members": orjson.dumps([hamlet.id]).decode(),
+            "description": "Test empty group",
+        }
+        result = self.client_post("/json/user_groups/create", info=params)
+        self.assert_json_error(result, "User group name can't be empty!")
+        self.assert_length(UserGroup.objects.filter(realm=hamlet.realm), 10)
+
         # Test invalid prefixes for user group name.
         params = {
             "name": "@test",
@@ -480,6 +490,11 @@ class UserGroupAPITestCase(UserGroupTestCase):
         result = self.client_patch(f"/json/user_groups/{user_group.id}", info=params)
         self.assert_json_error(result, "User group name cannot exceed 100 characters.")
 
+        # Test emtpty group name.
+        params = {"name": ""}
+        result = self.client_patch(f"/json/user_groups/{user_group.id}", info=params)
+        self.assert_json_error(result, "User group name can't be empty!")
+
         # Test invalid prefixes for user group name.
         params = {"name": "@test"}
         result = self.client_patch(f"/json/user_groups/{user_group.id}", info=params)