code: public void errorFuture(UUID taskId, Exception e) {
          DistributedFuture<GROUP, Serializable> future = remove(taskId);
          if(future != null) {
              future.setException(e);
          }
      }
docs: handles when a member leaves and hazelcast partition data is lost.  We want
  to find the Futures that are waiting on lost data and error them