CBPDocumentService::getFieldValue

public function getFieldValue($parameterDocumentId, $fieldId, $parameterDocumentType = null)
{
	[$moduleId, $entity, $documentId] = CBPHelper::ParseDocumentId($parameterDocumentId);
	$documentType = ($parameterDocumentType && is_array($parameterDocumentType)) ? $parameterDocumentType[2] : null;

	if ($moduleId)
	{
		CModule::IncludeModule($moduleId);
	}
	if (class_exists($entity) && method_exists($entity, 'getFieldValue'))
	{
		return call_user_func_array([$entity, "getFieldValue"], [$documentId, $fieldId, $documentType]);
	}

	$document = $this->GetDocument($parameterDocumentId, $parameterDocumentType);

	return $document[$fieldId] ?? null;
}