`deep.update` is not working if a link does not have a value

Minimal reproduction example:
```js
const {data: [{id: newLinkId}]} = await deep.insert({type_id: 22})
await deep.update(newLinkId, { value: 'abc' }, { table: 'strings' });
await deep.select(newLinkId)
```

Workaround:
```js
await deep.insert({link_id:876 , value: "name"},{table: "strings"})
await deep.insert({link_id: 877, value: {a: 1}}, {table: "objects"})
```

Start by running the JavaScript minimal reproduction for deep.insert, deep.update, and deep.select, then trace the deep.update entry point and the strings table path. Confirm how links without an existing value are handled. Done means updating the new link with value "abc" succeeds and deep.select returns the updated value without requiring the documented workaround.

Written by the indexing model from the issue text.