public function readFileLine($length = null)
    {
        $this->openFile();
        //gets warning "fgets(): Length parameter must be greater than 0" when parameter is null and is passed to function
        if($length === null)
        {
            $line = fgets($this->getFile());
        }
        else
        {
            $line = fgets($this->getFile(), $length);
        }

        return $line;
    }