title: Mule MEL, how to get a property value?
body: <p>In the Mule MEL, how to get a property value ? </p>
  
  <p>In the java code, I did this:</p>
  
  <pre><code>eventContext.getMessage().setInvocationProperty("amount", 100);
  </code></pre>
  
  <p>I have tried these options</p>
  
  <pre><code>#[message.invocationProperty.invocation]
  #[message.invocationProperty('invocation')]
  #[message.getInvocationProperty().get('invocation')]
  </code></pre>
  
  <p>I realize that message is an instance of org.mule.el.context.MessageContext, then what is the correct syntax ?</p>