public function prepend($k, $v = null)
    {
        $array = $this->val();

        if (!$this->isNull($v)) {
            $array = array_reverse($array, true);
            $array[$k] = $v;
            $array = array_reverse($array, true);
        } else {
            array_unshift($array, $k);
        }

        $this->val($array);

        return $this;
    }