Update migrations/MANUAL-fix-usernames-6b042b.py

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: Kulv3r

migrations/MANUAL-fix-usernames-6b042b.py

@@ -34,10 +34,7 @@ def upgrade(self, session):
         expression = """
             UPDATE iam_users
             SET 
-                email = CASE 
-                            WHEN email IS NULL THEN name
-                            ELSE email
-                        END,
+                email = COALESCE(email, name),
                 name = SUBSTRING(name, 1, POSITION('@' IN name) - 1)
             WHERE name LIKE '%@%';
         """