// do the actual merge here on the master, and update the mapping source
DocumentMapper newMapper = entry.getValue();
if (existingMappers.containsKey(entry.getKey())) {
// we have an existing mapping, do the merge here (on the master), it will automatically update the mapping source
DocumentMapper existingMapper = existingMappers.get(entry.getKey());
CompressedString existingSource = existingMapper.mappingSource();
existingMapper.merge(newMapper, mergeFlags().simulate(false));
CompressedString updatedSource = existingMapper.mappingSource();
if (existingSource.equals(updatedSource)) {