protected function processParts(array $parts)
    {
        $strValue = '';
        $ret = [];
        $filtered = $this->filterIgnoredSpaces($parts);
        foreach ($filtered as $part) {
            if ($part instanceof CommentPart) {
                $ret[] = $part;
                continue;    // getValue() is empty anyway, but for clarity...
            }
            $strValue .= $part->getValue();
        }
        array_unshift($ret, $this->partFactory->newReceivedPart($this->getPartName(), $strValue));
        return $ret;
    }