function cephadm::ssh_keys (
    Stdlib::Host $cephadm_controller,
) >> String[1] {
    $pql = @("PQL")
        inventory[facts.cephadm.ssh.key] {
            certname = "${cephadm_controller}"
        }
        | PQL
    wmflib::puppetdb_query($pql).reduce('') |$memo, $res| {
        "${memo}${res['facts.cephadm.ssh.key']}\n"
    }
}

Error: Evaluation Error: Error while evaluating a Function Call, 859: unexpected token at 'PQL parse error at line 1, column 34:

inventory[facts.cephadm.ssh.key] {
                                 ^

Expected one of:

]