presto-main/src/main/java/io/prestosql/operator/scalar/MapToMapCast.java/MapToMapCast/MapToMapCast
class MapToMapCast:    public MapToMapCast()
    {
        super(CAST,
                ImmutableList.of(
                        castableToTypeParameter("FK", new TypeSignature("TK")),
                        castableToTypeParameter("FV", new TypeSignature("TV")),
                        typeVariable("TK"),
                        typeVariable("TV")),
                ImmutableList.of(),
                mapType(new TypeSignature("TK"), new TypeSignature("TV")),
                ImmutableList.of(mapType(new TypeSignature("FK"), new TypeSignature("FV"))),
                true);
    }