Maybe_ generate wrong (non intuitive) sql query

I have left and right table, where right table contains nullable fields \
I join them with `leftJoin_` and try to create `filter_` which has such condition:
```haskell
maybe_ nothing_ nullableFieldFromRightTable rt /=. just_ (val_ 1)
```

So, if `rt` is null just return `nothing` and if `rt` is not null return `nullableFieldFromRightTable` which will return `nothing` or `just value` \
I am using it as beam doen't support to check nested maybes\
Then I just check if it is different from `just 1`\
This code compiles but I get invalid result, so, here is why:

```sql
CASE
WHEN ((((("t1"."someField1") IS NOT NULL) AND (("t1"."someField2") IS NOT NULL)) AND
(("t1"."nullableFieldFromRightTable") IS NOT NULL)) AND IS NOT NULL)
THEN "t1"."nullableFieldFromRightTable"
ELSE null END) IS DISTINCT FROM 1)
```
Beam generates strange query which doesn't the meaning of the beam query