docs: public CustomAttribute createCustomAttribute(final Object userIdOrUsername, final String key, final String value) throws GitLabApiException {
  
          if (Objects.isNull(key) || key.trim().isEmpty()) {
              throw new IllegalArgumentException("Key can't be null or empty");
          }
          if (Objects.isNull(value) || value.trim().isEmpty()) {
              throw new IllegalArgumentException("Value can't be null or empty");
          }
  
          GitLabApiForm formData = new GitLabApiForm().withParam("value", value);
          Response response = put(Response.Status.OK, formData.asMap(),
                  "users", getUserIdOrUsername(userIdOrUsername), "custom_attributes", key);
          return (response.readEntity(CustomAttribute.class));
      }