This question, as of this moment, has a "null" tag. There are four tag "buttons": linux, tools, "null", and threads.
"Retag" simply shows two spaces between "tools" and "threads".
Didn't try to fix it to allow troubleshooting.
That tag was
belongs-on-serverfault when the question was on SO. Apparently something went wrong with the auto-removal of
Maybe Jeff is stripping out the "belongs-on-" tags that questions have before they get migrated which is creating an empty tag.
This might get fixed by the daily vote sync script.