presto-main/src/main/java/io/prestosql/operator/scalar/MapToMapCast.java/MapToMapCast/checkDoubleIsNotNull
class MapToMapCast:    @UsedByGeneratedCode
    public static double checkDoubleIsNotNull(Double value)
    {
        if (value == null) {
            throw new PrestoException(INVALID_CAST_ARGUMENT, "map key is null");
        }
        return value;
    }