public static <T> ApiResponse<T> NotOk(String errorMessage) {
   ApiResponse<T> response = new ApiResponse<>();
   response.success = false;
   response.data = null;
   response.errorMessage = errorMessage;
   return response;
 }
 /*
  * Returns successful API call result.
  * */
 public static <T> ApiResponse<T> Ok(T data) {
   ApiResponse<T> response = new ApiResponse<>();
   response.success = true;
   response.data = data;
   return response;
 }