Impossible to add a Json object via the REST API

[Rafiot]

It only works with an XML object, not with a JSON one.

Code used to test: https://github.com/CIRCL/PyMISP/blob/master/pymisp/testing.py

The error mentioned an invalid event.

[iglocska]

Indeed, it's a bug with the JSON view erroneously including some related objects (such as threatlevel - instead of just including the ID). I'll push a fix later today.