presto-rcfile/src/main/java/io/prestosql/rcfile/text/TextRcFileEncoding.java/TextRcFileEncoding/mapEncoding
class TextRcFileEncoding:    @Override
    public ColumnEncoding mapEncoding(Type type, ColumnEncoding keyEncoding, ColumnEncoding valueEncoding)
    {
        return new MapEncoding(
                type,
                nullSequence,
                separators,
                escapeByte,
                (TextColumnEncoding) keyEncoding,
                (TextColumnEncoding) valueEncoding);
    }