[BUG]: rqb-v2 - Filtering breaks with filters { field: null }

### Report hasn't been filed before.

- [x] I have verified that the bug I'm about to report hasn't been filed before.

### What version of `drizzle-orm` are you using?

drizzle-orm-1.0.0-beta.15-859cf75

### What version of `drizzle-kit` are you using?

n/a

### Other packages

_No response_

### Describe the Bug

When I query (using rqb-v2) and I want to filter for a field being null, drizzle throws an error

```js
this.drizzle.query.table.findMany({
where: {
field: null
},
});
```

```log
[2026-03-01 13:07:28.203 -0300] ERROR: Cannot convert undefined or null to object {"reqId":"1abe221c-6d97-4790-9b60-191db0a5d2bc","context":"ExceptionsHandler"}
err: {
"type": "Error",
"message": "Cannot convert undefined or null to object",
"stack":
TypeError: Cannot convert undefined or null to object
at Function.entries ()
at relationsFieldFilterToSQL (/path/to/project/node_modules/src/relations.ts:1263:25)
at relationsFilterToSQL (/path/to/project/node_modules/src/relations.ts:1427:24)
at PgDialect.buildRelationalQuery (/path/to/project/node_modules/src/pg-core/dialect.ts:1050:14)
at PgAsyncRelationalQuery._getQuery (/path/to/project/node_modules/src/pg-core/query-builders/query.ts:115:23)
at PgAsyncRelationalQuery._toSQL (/path/to/project/node_modules/src/pg-core/query-builders/query.ts:130:22)
at (/path/to/project/node_modules/src/pg-core/async/query.ts:29:39)
at Object.startActiveSpan (/path/to/project/node_modules/src/tracing.ts:27:11)
at PgAsyncRelationalQuery._prepare (/path/to/project/node_modules/src/pg-core/async/query.ts:28:17)
at (/path/to/project/node_modules/src/pg-core/async/query.ts:60:16)
}
```

If the field is anything other than **null**, it works (falling back to the **"eq"** operator)

There is a workaround for that which is to use the **isNull** operator
```js
this.drizzle.query.table.findMany({
where: {
field: { isNull: true }
},
});
```

I'm wondering if this is expected or if **null** values should behave like other values fallback to the **"eq"** operator

Start with relations.ts at relationsFieldFilterToSQL, then follow its caller relationsFilterToSQL and the PgDialect relational-query path shown in the stack trace. Reproduce the rqb-v2 findMany query with { field: null }, compare it with the isNull workaround, and confirm that null filtering completes without the reported TypeError and has the agreed behavior.

Written by the indexing model from the issue text.