Wrapped entity must not be null exception on 204 No Content

I forgot to mention that assertions like Valid HTTP Status Codes works just fine and I can also access the response data using script assertions like:

String actual = new String(messageExchange.responseHeaders["Content-Type"].getAt(0).toString())
String expected = "application/json; charset=utf-8";
assert actual.equals( expected ), "Actual Content-Type: '" + actual + "' does not match expected: '" + expected + "'";

So the only problem is with displaying it inside of the window.

Cheers,
JK