@SuppressFBWarnings("NP_NONNULL_PARAM_VIOLATION") // Not a bug
  synchronized CompletableFuture<Void> getFutureForSequenceNumber(final long seqNum) {
    if (seqNum <= lastCompletedSequenceNumber) {
      return CompletableFuture.completedFuture(null);
    }
    return sequenceNumberFutures.computeIfAbsent(seqNum, k -> new CompletableFuture<>());
  }
@Test
  public void shouldReturnFutureForNewSequenceNumber() {
    // When:
    final CompletableFuture<Void> future = futureStore.getFutureForSequenceNumber(2);

    // Then:
    assertFutureIsNotCompleted(future);
  }