Naming strategy stops being respected in some cases

I just reproduced on an instance left running but not used on a laptop that was running and put to sleep on and off for three days.

this.validaton was null at this point. I first suspected that extension upgrades might be reloading the
XWikiConverter class without calling its initialize method, but I can't reproduce this: initialize is called.
 
For now, I will test for null and reset the naming strategy manager when it's null.
 
We don't know why it becomes null, but this workaround should hide the problem.