Error message dialog window for 'hg push' refers to git ref-format rules

While pushing update for mercurial repository, specifying branch and revision number (force push not ticked), resulted in an error popup dialog window that showed the command run but talked about git name formats (I replaced branch and revision from the actual error message by placeholder values for privacy):

hg push -b BRANCHNAME -r 11111 --new-branch default

One or more of this task's arguments is invalid. They cannot start with '-', and must follow git ref-format rules: https://www.kernel.org/pub/software/scm/git/docs/git-check-ref-format.html

Completed with errors, see above