@Override public void onSuccess(V value) {
          try {
            (mapped = flatMapper.map(value)).enqueue(callback);
          } catch (Throwable t) {
            propagateIfFatal(t);
            callback.onError(t);
          }
        }
Returns a copy of this object, so you can make an identical follow-up request.
zipkin/src/main/java/zipkin2/Call.java