private void mergeKeys(Key mergeInto, Key mergeFrom, KeyNameMapper sourceNameMapper, KeyNameMapper targetNameMapper) { Set<String> sourceFields = sourceNameMapper.getFieldSet(); sourceFields.removeAll(targetNameMapper.getFieldSet()); if(!sourceFields.isEmpty()) { for(String sourceField : sourceFields) { targetNameMapper.addMappedField(sourceField); mergeInto.addKey(targetNameMapper, sourceField, mergeFrom); } } } }