public function dumpString(): string
    {
        if ($this->header === null) {
            $this->header = new PoHeader;
            $this->header->buildDefaultHeader();
        }
        $output = '';

        $output .= $this->header->dumpEntry();
        foreach ($this->entries as $entry) {
            $output .= $entry->dumpEntry();
        }
        foreach ($this->unkeyedEntries as $entry) {
            $output .= $entry->dumpEntry();
        }
        $output .= "\n";

        return $output;
    }