presto-main/src/main/java/io/prestosql/operator/scalar/MapHashCodeOperator.java/MapHashCodeOperator/MapHashCodeOperator
class MapHashCodeOperator:    private MapHashCodeOperator()
    {
        super(HASH_CODE,
                ImmutableList.of(comparableTypeParameter("K"), comparableTypeParameter("V")),
                ImmutableList.of(),
                BIGINT.getTypeSignature(),
                ImmutableList.of(mapType(new TypeSignature("K"), new TypeSignature("V"))),
                false);
    }