docs: private void processFCM(AndroidVariant androidVariant, List<String> pushTargets, Message fcmMessage, ConfigurableFCMSender sender) throws IOException {
  
  
          // push targets can be registration IDs OR topics (starting /topic/), but they can't be mixed.
          if (pushTargets.get(0).startsWith(Constants.TOPIC_PREFIX)) {
  
              // perform the topic delivery
  
              for (String topic : pushTargets) {
                  logger.info(String.format("Sent push notification to FCM topic: %s", topic));
                  Result result = sender.sendNoRetry(fcmMessage, topic);
  
                  logger.trace("Response from FCM topic request: {}", result);
              }
          } else {
              logger.info(String.format("Sent push notification to FCM Server for %d registrationIDs", pushTargets.size()));
              MulticastResult multicastResult = sender.sendNoRetry(fcmMessage, pushTargets);
  
              logger.trace("Response from FCM request: {}", multicastResult);
  
              // after sending, let's identify the inactive/invalid registrationIDs and trigger their deletion:
              cleanupInvalidRegistrationIDsForVariant(androidVariant.getVariantID(), multicastResult, pushTargets);
          }
      }