NPE in AtomPojoProvider when no content (or content is empty)

When using the AtomPojoProvider with JAX-RS - the library bombs with an NPE (embedded in a ClientErrorException) if using JAXB annotated content objects - but no content is provided in the entry. It also NPE's if the content element is present but contains no XML (although this is a slightly dubious Atom document at this point).

Returning "null" would be a much better result in this case.