public void checkClientNamespaceExist(final String namespaceId) {
        NamespaceVO namespaceVO = namespaceService.findByNamespaceId(namespaceId);
        if (Objects.isNull(namespaceVO)) {
            throw new IllegalArgumentException("namespaceId is not exist");
        }
    }
Offline result string.

@param offlineDTO the offline dto
@return the string
shenyu-admin/src/main/java/org/apache/shenyu/admin/controller/ShenyuClientHttpRegistryController.java