presto-main/src/main/java/io/prestosql/operator/scalar/SplitToMapFunction.java/SplitToMapFunction/SplitToMapFunction
class SplitToMapFunction:    public SplitToMapFunction(@TypeParameter("map(varchar,varchar)") Type mapType)
    {
        pageBuilder = new PageBuilder(ImmutableList.of(mapType));
    }