<?php
$wc = new MongoDB\Driver\WriteConcern(1);
var_dump($wc->getJournal());
$wc = new MongoDB\Driver\WriteConcern(1, 0, true);
var_dump($wc->getJournal());
$wc = new MongoDB\Driver\WriteConcern(1, 0, false);
var_dump($wc->getJournal());
?>
The above example will output:
NULL
bool(true)
bool(false)