Fix wrong logic to get skip expression from receive task

modules/flowable-bpmn-converter/src/main/java/org/flowable/bpmn/converter/ReceiveTaskXMLConverter.java

@@ -55,7 +55,7 @@ protected BaseElement convertXMLToElement(XMLStreamReader xtr, BpmnModel model)
 
     @Override
     protected void writeAdditionalAttributes(BaseElement element, BpmnModel model, XMLStreamWriter xtw) throws Exception {
-        ReceiveTask receiveTask = new ReceiveTask();
+        ReceiveTask receiveTask = (ReceiveTask) element;
         writeQualifiedAttribute(ATTRIBUTE_TASK_SCRIPT_SKIP_EXPRESSION, receiveTask.getSkipExpression(), xtw);
     }