presto-redis/src/main/java/io/prestosql/plugin/redis/RedisRecordCursor.java/RedisRecordCursor/isNull
class RedisRecordCursor:    @Override
    public boolean isNull(int field)
    {
        checkArgument(field < columnHandles.size(), "Invalid field index");
        return currentRowValues == null || currentRowValues[field].isNull();
    }