ROutputParser is parsing NA as 0

Hi,
please check this function:

    public function singleNumber($output)
    {
        //TODO properly check if r output is a valid number
        return 0 + substr($output, 4);
    }

The problem is that if the return from R is like this:
[0] NA
the script will return "0".
But 0 is something else than NA, right?

gb5256