291 votesAnonymous commented
Yes, annoying bug. But there is a quick manual fix:
1) Drag the slicer field into the Page level filters
2) The default "Basic" filtering should show that there are no actual blanks
3) Choose Advanced and then choose "Is not blank"
This removes the blank option from the slicer and doesn't affect your data since there were no actual blanks.
This work is in progress!