Possible "Failed to evaluate the Velocity code from the query" error when using DBList properties with Velocity

There are actually two bugs:

• ExplicitlyAllowedValuesDBListQueryBuilder#build produce a null "namespace" which is not the intent of the code at all, that one is an old bug (XWIKI-14700 or most probably even before)
• the velocity engine does not accept null namespace anymore (because a null namespace name can cause problem) but it should fallback on an arbitrary namespace name (which is what it used to do but which has been broken) - fixed in XCOMMONS-2877