private function addToSplitPart(ArrayObject $splitParts, $name, $value, $index, $isEncoded)
    {
        $ret = null;
        if (!isset($splitParts[trim($name)])) {
            $ret = $this->partFactory->newSplitParameterToken($name);
            $splitParts[$name] = $ret;
        }
        $splitParts[$name]->addPart($value, $isEncoded, $index);
        return $ret;
    }