code: public void addAll(GlobalMetadata other) {
      throwIfImmutable();
  
      datasetLevel.putAll(other.datasetLevel);
      for (Map.Entry<String, Map<String, Object>> e : other.fileLevel.entrySet()) {
        Map<String, Object> val = new ConcurrentHashMap<>();
        val.putAll(e.getValue());
        fileLevel.put(e.getKey(), val);
      }
  
      cachedId = null;
    }
docs: Merge another GlobalMetadata object into this one. All keys from 'other' will be placed into
  this object, replacing any already existing keys.
  @param other Metadata object to add