MessageBodyWriter not found!

I got the following (unhelpful) message in my server log, when I changed some of my Java classes that are translated to JSON (and vice versa).

Severe: MessageBodyWriter not found for media type=application/json, type=class java.util.ArrayList, genericType=java.util.List

Turns out that I added a specific constructor to one of my Java classes, effectively removing the unspecified Default Constructor that Java always adds.

This default constructor is however essential to the proper working of JSON-Java mapping.