PayrollReportController.php

<?php

function replacer($array) {
    $newArray = array();
    
    foreach ($array as $key => $val) {
        foreach ($val as $k=>$v) {
            if ($v == "" || $v === null) {
                $newArray[$key][$k] = "empty";
            } else {
                $newArray[$key][$k] = $v;
            }
        }
    }
    
    return $newArray;
}

$res = $this->replacer($res);