diff --git a/src/main/java/de/hsfulda/informatik/LdapSync.java b/src/main/java/de/hsfulda/informatik/LdapSync.java
index 1188e40..a63c0b2 100644
--- a/src/main/java/de/hsfulda/informatik/LdapSync.java
+++ b/src/main/java/de/hsfulda/informatik/LdapSync.java
@@ -178,6 +178,10 @@ public class LdapSync {
                 }
             }
 
+            if (m.group(2).isEmpty()) {
+                return null;
+            }
+
             final int s = m.group(2).length();
             final int z = Integer.parseInt(m.group(2));