title: how to reference a flow variable in an expression filter?
body: <p>How to reference a flow variable in an expression filter?</p>
  
  <p>Assuming that <code>myVariable</code> is a boolean, I tried:</p>
  
  <pre><code>&lt;expression-filter evaluator="variable" expression="myVariable" /&gt;
  </code></pre>
  
  <p>but that did not work. Eventually I settled for:</p>
  
  <pre><code>&lt;expression-filter evaluator="groovy" expression="message.getInvocationProperty('myVariable')" /&gt;
  </code></pre>
  
  <p>Thanks</p>