private function setCustomFields()
    {
        $customFieldCollection = new CustomFieldCollection();

        if (isset($this->simpleXml->{'custom-fields'})) {
            /** @var SimpleXMLElement $field */
            foreach ($this->simpleXml->{'custom-fields'}->children() as $field) {
                $customField = $this->convertToCustomField($field);
                if (!is_null($customField)) {
                    $customFieldCollection->add($customField);
                }
            }
        }
        $this->customFields = $customFieldCollection;
    }