Index: Target.js
===================================================================
--- Target.js	(Revision 4224)
+++ Target.js	(Arbeitskopie)
@@ -55,6 +55,10 @@
   if(this._disposed) {
     return;
   }
+  
+  if (qx.util.Validation.isInvalidString(vType)) {
+  	throw new Error("qx.core.Target.addEventListener: vType is nor a valid string!");
+  }
 
   if(typeof vFunction !== qx.constant.Type.FUNCTION) {
     throw new Error("qx.core.Target: addEventListener(" + vType + "): '" + vFunction + "' is not a function!");