Bug#689815: devscripts: [bts] cannot remove all usertags from bug

[Benjamin Drung]

Package: devscripts
Version: 2.12.4
Severity: normal

Dear Maintainer,

the man page of bts says: "At least one tag must be specified, unless the =
flag is used, where the command

    bts usertags <bug> =

will remove all user tags from the specified bug."

I tried to remove all user tags from one bug with following command:

    $ bts usertags 688060 =
    bts usertags: set what user tag?

bts throws an error instead of removing all user tags.