将PDO :: FETCH_ASSOC结果分配给$ _SESSION变量

Question

I have a login page that collects clients mapped a certain user upon login.

            $query_acct = "select client from app_reports.user_map where user_name = '".$username."'";
            $acct = $DB_con->prepare($query_acct);
            $acct->execute();
            $row_acct = $acct->fetchAll(PDO::FETCH_ASSOC);
            if (!empty($row_acct['client'])){
                foreach($row_acct as $r) {
                    $client[] = $r['client'];
                    }
                $_SESSION['client'] = $client;
                    }

As I understood it, $_SESSION['client'] should store the array stored in $client. But when I attempted to print it out with:

foreach($_SESSION['client'] as $key=>$value){

    // and print out the values
    echo 'The value of $_SESSION['."'".$key."'".'] is '."'".$value."'".' <br />';

}

I'm getting: Notice: Undefined index: client

Warning: Invalid argument supplied for foreach()

I'd like to get some advice on how to store an array in a session properly so I can print them out (will be used as a dropdown, etc.)