Critical plugin error

Hello,
I’m working with your plugin and I have saw, that you have a method, which use undefined variable.

Check you file: plugins/webp-express/lib/classes/HandleUploadHooks.php line 82.

Method:

public static function handleMakeIntermediateSize($filename)
    {
        if (!is_null($filename)) {
            try {
                $filenameToConvert = SanityCheck::absPathExistsAndIsFileInDocRoot($filearray['file']);
                    self::convertIf($filenameToConvert);
            } catch (SanityException $e) {
                // fail silently. (maybe we should write to debug log instead?)
            }
        }
        return $filename;
    }

Where variable $filearray[‘file’] defined??

Please, make a fix ??