title: SignalExpression in Activiti 6.0 Intermediate Catching event
body: <p>I am trying to create a process with the Intermediate Catching event with conditional expression. I can see that <code>SignalEventDefinition</code> has a property called <code>signalExpression</code>. But somehow I am not able to use it.</p>
  
  <p>Here is the code from BaseBpmnXMLConverter.</p>
  
  <pre><code>protected void writeSignalDefinition(Event parentEvent, SignalEventDefinition signalDefinition, XMLStreamWriter xtw) throws Exception {
      xtw.writeStartElement(ELEMENT_EVENT_SIGNALDEFINITION);
      writeDefaultAttribute(ATTRIBUTE_SIGNAL_REF, signalDefinition.getSignalRef(), xtw);
      if (parentEvent instanceof ThrowEvent &amp;&amp; signalDefinition.isAsync()) {
        BpmnXMLUtil.writeQualifiedAttribute(ATTRIBUTE_ACTIVITY_ASYNCHRONOUS, "true", xtw);
      }
      boolean didWriteExtensionStartElement = BpmnXMLUtil.writeExtensionElements(signalDefinition, false, xtw);
      if (didWriteExtensionStartElement) {
        xtw.writeEndElement();
      }
      xtw.writeEndElement();
    }
  </code></pre>
  
  <p>I don't see how can we create signalExpression inside <code>signalEventDefinition</code>.</p>
  
  <p>I can even see the signalExpression is considered in <code>IntermediateCatchSignalEventActivityBehavior</code> as well as in <code>EventValidator</code>. So It looks like I don't know how to use signalExpression inside catching event. Can someone please help me find the right way.</p>
  
  <p>I am using Activiti 6.0 and my own custom UI to create BPMN model which in turn calls activiti-bpmn-converter to generate the process definition XML.</p>