private function getHeaderPrefix(array $data)
    {
        if ($this->first && $this->csvFormat->hasHeaderRow()) {
            $this->first = false;
            $postHeaderPad = $this->csvFormat->getDataStart() - $this->csvFormat->getHeaderRow();
            return $this->format(array_keys($data)) . str_repeat($this->getRowSeparator(), $postHeaderPad);
        }
        return '';
    }