code: private void setupOAD() {
          BluetoothGattService oadService = mGattClient.getService(Constants.UUID_OAD_SERVICE);
          if (oadService == null) {
              fail(BeanError.MISSING_OAD_SERVICE);
              return;
          }
  
          oadIdentify = oadService.getCharacteristic(Constants.UUID_OAD_CHAR_IDENTIFY);
          if (oadIdentify == null) {
              fail(BeanError.MISSING_OAD_IDENTIFY);
              return;
          }
  
          oadBlock = oadService.getCharacteristic(Constants.UUID_OAD_CHAR_BLOCK);
          if (oadBlock == null) {
              fail(BeanError.MISSING_OAD_BLOCK);
              return;
          }
      }
docs: Setup BLOCK and IDENTIFY characteristics