docs: public void deleteCustomAttribute(final Object userIdOrUsername, final String key) throws GitLabApiException {
  
          if (Objects.isNull(key) || key.trim().isEmpty()) {
              throw new IllegalArgumentException("Key can't be null or empty");
          }
  
          delete(Response.Status.OK, null, "users", getUserIdOrUsername(userIdOrUsername), "custom_attributes", key);
      }