@Override
  public void merge(final Mapper mergeWith, final MergeContext mergeContext)
      throws MergeMappingException {
    if (!(mergeWith instanceof ObjectMapper)) {
      mergeContext.addConflict(
          "Can't merge a non object mapping ["
              + mergeWith.name()
              + "] with an object mapping ["
              + name()
              + "]");
      return;
    }
    ObjectMapper mergeWithObject = (ObjectMapper) mergeWith;

    doMerge(mergeWithObject, mergeContext);

    List<Mapper> mappersToTraverse = new ArrayList<Mapper>();
    synchronized (mutex) {
      for (Mapper mergeWithMapper : mergeWithObject.mappers.values()) {
        Mapper mergeIntoMapper = mappers.get(mergeWithMapper.name());
        if (mergeIntoMapper == null) {
          // no mapping, simply add it if not simulating
          if (!mergeContext.mergeFlags().simulate()) {
            putMapper(mergeWithMapper);
            mappersToTraverse.add(mergeWithMapper);
          }
        } else {
          if ((mergeWithMapper instanceof MultiFieldMapper)
              && !(mergeIntoMapper instanceof MultiFieldMapper)) {
            MultiFieldMapper mergeWithMultiField = (MultiFieldMapper) mergeWithMapper;
            mergeWithMultiField.merge(mergeIntoMapper, mergeContext);
            if (!mergeContext.mergeFlags().simulate()) {
              putMapper(mergeWithMultiField);
              // now, record mappers to traverse events for all mappers
              for (Mapper mapper : mergeWithMultiField.mappers().values()) {
                mappersToTraverse.add(mapper);
              }
            }
          } else {
            mergeIntoMapper.merge(mergeWithMapper, mergeContext);
          }
        }
      }
    }
    // call this outside of the mutex
    for (Mapper mapper : mappersToTraverse) {
      mapper.traverse(
          new FieldMapperListener() {
            @Override
            public void fieldMapper(FieldMapper fieldMapper) {
              mergeContext.docMapper().addFieldMapper(fieldMapper);
            }
          });
      mapper.traverse(
          new ObjectMapperListener() {
            @Override
            public void objectMapper(ObjectMapper objectMapper) {
              mergeContext.docMapper().addObjectMapper(objectMapper);
            }
          });
    }
  }