Query data is {} instead of undefined, despite pull request 3388

[strblr]

Intended outcome:
According to apollographql/react-apollo#3388, unavailable data should not be {} but undefined. One reason mentioned in the PR makes a lot of sense (especially using codegen) :

Forcing no data situations to be empty objects can go against application schemas that enforce a value and don't allow empty objects.

Actual outcome:
It's actually still {} between refetches, when nothing's found in the cache, essentially giving two different semantics for "there's no data" : undefined on initial fetch, then {}. This feels inconsistent and generates nasty runtime errors that are not catched by TypeScript when using codegen.

It also makes patterns like these (recommended here : #6603 (comment)) pointless :

const continuousData = data ?? previousData

How to reproduce the issue:

• CodeSandbox Link
  Let the first page load, then move to another page. Finally, read the data value in the console :

undefined
{todos: Object}
{todos: Object}
{}
{todos: Object}

Versions
@apollo/client: ^3.3.6 => 3.3.6

[gbiryukov]

I believe this issue is caused by this snippet.
Seems it had to be removed in this PR to follow currently documented behavior.

A workaround is to disable notifyOnNetworkStatusChange which is not possible in all cases.

[strblr]

Seems it had to be removed in this PR to follow currently documented behavior.

Honestly, this PR was just such a bad idea. I switched to urql.

[hwillson]

Let us know if this is still a concern with @apollo/client@latest - thanks!