Index: /trunk/autoquest-plugin-uml/src/main/java/de/ugoe/cs/autoquest/plugin/uml/UMLUtils.java
===================================================================
--- /trunk/autoquest-plugin-uml/src/main/java/de/ugoe/cs/autoquest/plugin/uml/UMLUtils.java	(revision 1977)
+++ /trunk/autoquest-plugin-uml/src/main/java/de/ugoe/cs/autoquest/plugin/uml/UMLUtils.java	(revision 1978)
@@ -1072,8 +1072,7 @@
             String path = calledOperation.getName() + ":" + param.getType().getName();
             // create param node
-            Expression argument =
-                (Expression) callMessage.createArgument(param.getName(), param.getType(),
-                                                        UMLPackage.Literals.EXPRESSION);
-
+//            Expression argument =
+//                (Expression) callMessage.createArgument(param.getName(), param.getType(),
+//                                                        UMLPackage.Literals.EXPRESSION);
             if (isInParameter(param)) {
                 
@@ -1087,9 +1086,11 @@
                                                           UMLPackage.Literals.INSTANCE_SPECIFICATION);
                 instSpecParameters.getClassifiers().add((DataType) param.getType());
-                InstanceValue parametersValue =
-                        (InstanceValue) argument
-                            .createOperand(param.getType().getName(), param.getType(),
-                                           UMLPackage.Literals.INSTANCE_VALUE);
-                parametersValue.setInstance(instSpecParameters);
+//                InstanceValue parametersValue =
+//                        (InstanceValue) argument
+//                            .createOperand(param.getType().getName(), param.getType(),
+//                                           UMLPackage.Literals.INSTANCE_VALUE);
+//                parametersValue.setInstance(instSpecParameters);
+                InstanceValue instanceValue = (InstanceValue) callMessage.createArgument(param.getName(), param.getType(), UMLPackage.Literals.INSTANCE_VALUE);
+                instanceValue.setInstance(instSpecParameters);
                 
                 for( Property internalParameter : parametersNode.getAllAttributes() ) {
@@ -1141,5 +1142,6 @@
             else {
                 // set literalNull for out and return parameters
-                argument.createOperand(null, param.getType(), UMLPackage.Literals.LITERAL_NULL);
+//                argument.createOperand(null, param.getType(), UMLPackage.Literals.LITERAL_NULL);
+                callMessage.createArgument(param.getName(), param.getType(), UMLPackage.Literals.LITERAL_NULL);
             }
         }