code: protected <T, A> ActiveOperation<T, A> removeActiveOperation(Integer id) {
          final ActiveOperation<T, A> removed = removeUnderLock(id);
          if(removed != null) {
              for(final Map.Entry<Integer, ActiveRequest<?, ?>> requestEntry : requests.entrySet()) {
                  final ActiveRequest<?, ?> request = requestEntry.getValue();
                  if(request.context == removed) {
                      requests.remove(requestEntry.getKey());
                  }
              }
          }
          return removed;
      }
docs: Remove an active operation.
  
  @param id the operation id
  @return the removed active operation, {@code null} if there was no registered operation