diff --git a/src/main/java/org/minimalj/security/UserPasswordAuthentication.java b/src/main/java/org/minimalj/security/UserPasswordAuthentication.java
index <HASH>..<HASH> 100644
--- a/src/main/java/org/minimalj/security/UserPasswordAuthentication.java
+++ b/src/main/java/org/minimalj/security/UserPasswordAuthentication.java
@@ -129,7 +129,5 @@ public abstract class UserPasswordAuthentication extends Authentication {
 		}
 	}
 
-	protected User retrieveUser(String userName) {
-		return null;
-	}
+	protected abstract User retrieveUser(String userName);
 }
\ No newline at end of file
UserPasswordAuthentication: make empty method abstract