Current Behavior

If a existing user has no attributes, it is not possible to add attributes to it.

Expected Behavior

Updating of attributes existing user, which has no attributes set, should work.

Steps To Reproduce

1. Create a user without attributes.
2. Update user attributes (adding one or more attributes)
3. No attributes are set to the user.

Environment

• Keycloak Version: 26.1.0 (also verified with Keycloak 26.0.8)
• keycloak-config-cli Version: 6.3.0
• Java Version: Java 21

Anything else?

I have found out, that the Problem is located at the UserImportService. I fixed it and I will contribute the fix.