private function readCurrent() : void
    {
        $row = $this->readRow();

        if ($this->columns === null || $row === null) {
            $this->current = $row;
        } else {
            $this->current = [];

            foreach ($this->columns as $key => $name) {
                $this->current[$name] = isset($row[$key]) ? $row[$key] : null;
            }
        }
    }