presto-iceberg/src/main/java/io/prestosql/plugin/iceberg/util/PageListBuilder.java/PageListBuilder/appendVarcharVarcharMap
class PageListBuilder:    public void appendVarcharVarcharMap(Map<String, String> values)
    {
        BlockBuilder column = nextColumn();
        BlockBuilder map = column.beginBlockEntry();
        values.forEach((key, value) -> {
            VARCHAR.writeString(map, key);
            VARCHAR.writeString(map, value);
        });
        column.closeEntry();
    }