[Isomorphic]

We're not sure what you mean about how we check for that attribute. We parse the request according to its format, then we start processing it.

[rle125]

In my class that extends RESTHandler I added validation that the request has proper data ("dataSource" and "operationType") prior to calling super.processRequest().

HttpServletRequestWrapper allows me to read the request data and still pass it to super.processRequest() for processing.

[Isomorphic]

We already plan to change the reporting of this error so it's not just a plain NPE, but feel free to add a second layer of error checking, of course.