presto-rcfile/src/main/java/io/prestosql/rcfile/binary/MapEncoding.java/MapEncoding/MapEncoding
class MapEncoding:    public MapEncoding(Type type, BinaryColumnEncoding keyReader, BinaryColumnEncoding valueReader)
    {
        super(type);
        this.keyReader = keyReader;
        this.valueReader = valueReader;
    }