diff --git a/src/spaceone/identity/service/workspace_group_service.py b/src/spaceone/identity/service/workspace_group_service.py
index a05a342..b439e7d 100644
--- a/src/spaceone/identity/service/workspace_group_service.py
+++ b/src/spaceone/identity/service/workspace_group_service.py
@@ -564,6 +564,8 @@ def add_user_name_and_state_to_users(
                 "state": user_vo.state,
             }
 
+        if wg_users is None:
+            wg_users = []
         users = []
         for user in wg_users:
             if isinstance(user, dict):