non well formed numeric value

OwebiaShippingHelper.php

    public static function parseSize($size)
    {
        $strSize = trim($size);
        $last = strtolower($strSize[strlen($strSize)-1]);
        $size = rtrim($strSize, $last);
        switch ($last) {
            case 'g': $size *= 1024;
            case 'm': $size *= 1024;
            case 'k': $size *= 1024;
        }
        return (float)$size;
    }