Ok It makes sense that it is empty, but not null. I think null never comes but it is ok to check it.

Could you change the patch so instead of returning, embrace all the try-catch block in the if block, which should generate less code in gwt, I mean:

if (retData != null && !"".equals(retData) {
  try ...
}

Just make the changes and commit to the same branch and you don't have to send a new pull-request