Wysiwyg editor 2 does not handle well properties that return null

When a property is set to null on a textarea in wysiwyg mode in syntax 2.0, then the editor uses the content of the full document in the wysiwyg.

This is because of velocity not handling null well:

We need to preset in wysiwyginput.vm the content field to empty

#if($wysiwygInput && $wysiwygInput.containsKey($request.key))
#set($content = "")
#set($content = $wysiwygInput.get($request.key))
#set($ok = $wysiwygInput.remove($request.key))
#end