Fix -> operator on missing values to return null

[rkistner]

Using the -> operator with a missing value, for example select '{}' -> 'test', would return undefined instead of null. We use SQLite types, so there should never be an undefined value.

This was specifically an issue when used together with json_each, for example SELECT value as project_id FROM json_each(request.jwt() -> 'project_ids'). This query would throw an error Expected json_each to be called with a string, got undefined, instead of treating it like an empty array like with null values.

This fixes select '{}' -> 'test' to return null correctly.

This also adds tests for all the following forms:

select '{"t": null}' -> 't' -- null in PowerSync, 'null' in SQLite
select '{}' -> 't' -- null in PowerSync and SQLite, fixed by this PR

select '{"t": null}' ->> 't' -- 'null' in PowerSync, null in SQLite
select '{}' ->> 't' -- null in PowerSync and SQLite

select json_extract('{"t": null}', '$.t') -- 'null' in PowerSync, null in SQLite
select json_extract('{}', '$.t') -- null in PowerSync and SQLite

Notice the difference in handling of {"t": null} values between PowerSync and SQLite. That is not affected by this PR though, and fixing it to match SQLite would be a breaking change, so keeping it as-is for now.

[changeset-bot]

🦋 Changeset detected

Latest commit: a332599

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 10 packages

Name	Type
@powersync/service-sync-rules	Patch
@powersync/service-core-tests	Patch
@powersync/service-core	Patch
@powersync/service-module-mongodb-storage	Patch
@powersync/service-module-mongodb	Patch
@powersync/service-module-mysql	Patch
@powersync/service-module-postgres-storage	Patch
@powersync/service-module-postgres	Patch
@powersync/service-image	Patch
test-client	Patch

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