bonjour j'ai un proble avec mon code php

<?php
function get_posts(){
global $isc_lushi;
$req = $isc_lushi->query("SELECT * from posts");
$results= array();
while ($rows= $req->fetchObject()) {
$results[]= $rows;
}
return $results;
}
$posts= get_posts();
foreach ($posts as $post) {
?>
}
et le resultat ( ! ) Error: Call to a member function query() on null in C:\wamp64\www\isc_lushi\pages\home.php on line 4