Fix compiler error
diff --git a/org.eclipse.bpmn2.modeler.ui/src/org/eclipse/bpmn2/modeler/ui/adapters/properties/InterfacePropertiesAdapter.java b/org.eclipse.bpmn2.modeler.ui/src/org/eclipse/bpmn2/modeler/ui/adapters/properties/InterfacePropertiesAdapter.java
index 54a8d12..92a7869 100644
--- a/org.eclipse.bpmn2.modeler.ui/src/org/eclipse/bpmn2/modeler/ui/adapters/properties/InterfacePropertiesAdapter.java
+++ b/org.eclipse.bpmn2.modeler.ui/src/org/eclipse/bpmn2/modeler/ui/adapters/properties/InterfacePropertiesAdapter.java
@@ -99,7 +99,7 @@
 	    					prefix = NamespaceUtil.addNamespace(resource, qname.getNamespaceURI());
 	    				if (prefix!=null)
 	    					value = prefix + ":";
-	    				value += qname.getLocalPart();
+	    				value = value.toString() + qname.getLocalPart();
 	    			}
 	    			else if (value instanceof Process) {
 	    				Process process = (Process)value;