message: additional assert()
diff: @@ -34,6 +34,7 @@ public class IndyJava {
  protected static int addFuture(CompletableFuture<?> future) {
  int commandHandle = Integer.valueOf(atomicInteger.incrementAndGet());
  + assert(! futures.containsKey(Integer.valueOf(commandHandle)));
  futures.put(Integer.valueOf(commandHandle), future);
  return commandHandle;
  