title: MapStruct: How to pass input object to expression?
body: <p>In MapStruct version 1.1.0.Final, this was possible....</p>
  
  <pre><code>@Mappings({
      @Mapping(target = "transaction.process.details", expression = "java(MappingHelper.mapDetails(request))"),
       //more mappings
  })
  Response requestToResponse(Request request);
  </code></pre>
  
  <p>It was possible, since the <code>mapDetails</code> method was (by coincidence?) generated into the <code>requestToResponse</code> method. That's why <code>request</code> was not null. </p>
  
  <p>Now, since 1.1.0.Final didn't work with Lombok, I had to upgrade to 1.2.0.CR2. With this version, the <code>mapDetails</code> will be generated into a separate method where <code>request</code> is not passed, so <code>request</code> is null within this method now and I get a NPE with the expression. (It's a sub-sub-method of <code>requestToResponse</code> now.)</p>
  
  <p>Did I misuse the expression, so did it just work by coincidence, or does the new version has a bug? If no bug, how do I have to pass the <code>request</code> instance to the expression properly?</p>