diff --git a/formatters/user.py b/formatters/user.py
index 611fc52..50397b3 100644
--- a/formatters/user.py
+++ b/formatters/user.py
@@ -4,12 +4,16 @@
 
 
 def format_users(users: dict[str, Any], params: Optional[dict] = None) -> List[User]:
+    first_name = users.get('firstName') or ''
+    last_name = users.get('lastName') or ''
+    display_name = f"{first_name} {last_name}".strip() or users.get("username", "Unknown")
+    
     formatted_users = [
         User(
-            username=users.get("username"),
-            display_name=users.get('firstName') + " " + users.get('lastName'),
-            first_name=users.get('firstName'),
-            last_name=users.get('lastName'),
+            username=users.get("username") or "unknown",
+            display_name=display_name,
+            first_name=first_name,
+            last_name=last_name,
         )
     ]
     return formatted_users