def generate_user_and_server(server_address, ssh_user) -> str:
    """ Return user@server to be used with commands run over SSH.

    If ssh_user is not given, simply return the address of the server,
    assuming that the current user is suitable for running the command.
    """
    if ssh_user is None:
        return server_address
    return ssh_user + '@' + server_address