title: activiti execution.setvariable not working in task listener
body: <p>Good day.</p>
  
  <p>I created a variable instance 'TaskAssignee' which will be utilize across task and flow.
  TaskAssignee will store the task assignee name and show it in the next user task (via form).
  I used the execution.setVariable inside the task listener but it didn't work.
  How am i able to do it?</p>
  
  <p>Here is the code :</p>
  
  <pre><code>&lt;process id="GetAssigneePerTask2" name="Get Assignee Per Task" isExecutable="true"&gt;
  &lt;documentation&gt;undefined&lt;/documentation&gt;
  &lt;extensionElements&gt;
  &lt;activiti:executionListener event="start" expression="${execution.setVariable(&amp;quot;TaskAssignee&amp;quot;, &amp;quot;MyData&amp;quot;)}"/&gt;
  &lt;modeler:executionvariables xmlns:modeler="http://activiti.com/modeler" modeler:variableName="TaskAssignee" modeler:variableType="string"/&gt;
  &lt;/extensionElements&gt;
  &lt;startEvent id="startEvent1"/&gt;
      &lt;userTask id="sid-F533EC22-E107-49D2-ABDE-AE3BA402E8A4" name="Show Task User" activiti:assignee="$INITIATOR" activiti:formKey="2661"&gt;
        &lt;extensionElements&gt;
          &lt;modeler:allow-send-email&gt;true&lt;/modeler:allow-send-email&gt;
          &lt;modeler:form-reference-id&gt;2661&lt;/modeler:form-reference-id&gt;
          &lt;modeler:form-reference-name&gt;Show Data form&lt;/modeler:form-reference-name&gt;
          &lt;modeler:initiator-can-complete&gt;true&lt;/modeler:initiator-can-complete&gt;
        &lt;/extensionElements&gt;
      &lt;/userTask&gt;
      &lt;sequenceFlow id="sid-F6A4A4AA-3075-4FA2-BE69-5109B340E3A8" sourceRef="sid-CB8D41DC-E2C6-4D60-A247-62630B0EF758" targetRef="sid-F533EC22-E107-49D2-ABDE-AE3BA402E8A4"/&gt;
      &lt;endEvent id="sid-C23D6404-68B8-4C5C-8469-562C63E363AA"/&gt;
      &lt;sequenceFlow id="sid-70DA56B6-5156-4CF1-8B36-DE0CB28096C5" sourceRef="sid-F533EC22-E107-49D2-ABDE-AE3BA402E8A4" targetRef="sid-C23D6404-68B8-4C5C-8469-562C63E363AA"/&gt;
      &lt;userTask id="sid-CB8D41DC-E2C6-4D60-A247-62630B0EF758" name="Get User of this task" activiti:assignee="$INITIATOR"&gt;
        &lt;extensionElements&gt;
          &lt;activiti:taskListener event="complete" class="org.activiti.engine.impl.bpmn.listener.ScriptTaskListener"&gt;
            &lt;activiti:field name="script"&gt;
              &lt;activiti:string&gt;&lt;![CDATA[var dataValue = task.assignee;
  execution.setVariable("TaskAssignee", dataValue);]]&gt;&lt;/activiti:string&gt;
            &lt;/activiti:field&gt;
            &lt;activiti:field name="language"&gt;
              &lt;activiti:string&gt;&lt;![CDATA[javascript]]&gt;&lt;/activiti:string&gt;
            &lt;/activiti:field&gt;
          &lt;/activiti:taskListener&gt;
          &lt;modeler:allow-send-email&gt;true&lt;/modeler:allow-send-email&gt;
          &lt;modeler:initiator-can-complete&gt;true&lt;/modeler:initiator-can-complete&gt;
        &lt;/extensionElements&gt;
      &lt;/userTask&gt;
      &lt;sequenceFlow id="sid-9B8DB7EE-D9CD-4FA8-96C8-ED62ECED5404" sourceRef="startEvent1" targetRef="sid-CB8D41DC-E2C6-4D60-A247-62630B0EF758"/&gt;
    &lt;/process&gt;
  </code></pre>
  
  <p>BTW i'm using activiti 5.19.</p>