Slight inconsistency between ref delete commands.

Hello,

Was writing conversion script from CVS to git for my repo and noticed slight inconsistency in git-tag, git-branch, and git-update-ref behavior:

$ git --version
git version 1.9.3
$ git tag -d && echo success
success
$ git branch -d && echo success
fatal: branch name required
$ git update-ref -d && echo success
usage: git update-ref [options] -d <refname> [<oldval>]
   or: git update-ref [options]    <refname> <newval> [<oldval>]
   or: git update-ref [options] --stdin [-z]

    -m <reason>           reason of the update
    -d                    delete the reference
    --no-deref            update <refname> not the one it points to
    -z                    stdin has NUL-terminated arguments
    --stdin               read updates from stdin

Noticed when used xargs without -r switch, like this:

git for-each-ref --format="%(refname)" "refs/tags/*-merge" | xargs -n 1 git update-ref -d

-- Sergey.