tag: do not pass binary nullid to scmutil.revsingle()

Future patches will remove the old-style parser that happen to accept a
binary nodeid. A binary nodeid shouldn't be passed to scmutil.revrange()
because it is ambiguous. For example, bin('20' * 19 + '30') is valid binary
nodeid, but it can also be parsed as a revset expression, '0'.

mercurial/commands.py

@@ -6248,7 +6248,7 b' def tag(ui, repo, name1, *names, **opts)'
                         raise util.Abort(_("tag '%s' is not a global tag") % n)
                     else:
                         raise util.Abort(_("tag '%s' is not a local tag") % n)
-            rev_ = nullid
+            rev_ = 'null'
             if not message:
                 # we don't translate commit messages
                 message = 'Removed tag %s' % ', '.join(names)