code: private String generateSilientCheckpointId() {
          byte[] randomBytes = new byte[32];
          ThreadLocalRandom.current().nextBytes(randomBytes);
          return Base64.getEncoder().encodeToString(randomBytes) + SILENT;
      }
docs: Generate an internal Checkpoint Id. It is appended with a suffix {@link ReaderGroupImpl#SILENT} which ensures
  that the readers do not generate an event where {@link io.pravega.client.stream.EventRead#isCheckpoint()} is true.