public T addCol(String name, String type, String comment) {
    if (cols == null) cols = new ArrayList<>();
    cols.add(new FieldSchema(name, type, comment));
    return child;
  }
This collects together SerdeInfo and columns, since StorageDescriptor and SchemaVersion share
those traits.
@param <T>
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/client/builder/SerdeAndColsBuilder.java