`@` alias for `HEAD` not working in `git push -u origin @`

[Mark Florian <mflorian@xxxxxxxxxx>]

Hello!

I learned today that `@` is a shortcut for `HEAD`. From `git help reivisions`:

    @ alone is a shortcut for HEAD.

However, when I tried to use it in a command I frequently use, I got an error:

    $ git push -u origin @
    fatal: invalid refspec '@'

I'm running git version 2.22.0 on Linux.

Is this a bug, or have I misunderstood how this is supposed to work?

Cheers,
Mark