private List<MFieldSchema> convertToMFieldSchemas(List<FieldSchema> keys) {
    List<MFieldSchema> mkeys = null;
    if (keys != null) {
      mkeys = new ArrayList<>(keys.size());
      for (FieldSchema part : keys) {
        mkeys.add(new MFieldSchema(part.getName().toLowerCase(),
            part.getType(), part.getComment()));
      }
    }
    return mkeys;
  }
Makes shallow copy of a map to avoid DataNucleus mucking with our objects.
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/ObjectStore.java