I TRIM, you TRIM, he TRIMs
You never know whether the first one did not work. A TRIM forewarned is worth two.
if (isset($_GET['id_coll'])) $id_coll = trim($_GET['id_coll']);
else $id_coll = '';
if (trim($id_coll)!='' && is_numeric($id_coll))
{
......
}