Improve debugability of block plugins returning NULL in Layout Builder

It looks like \Drupal\block\BlockViewBuilder::preRender also explicitly adds support for NULL type, even though it's not documented to be supported. 😬 As the error suggests, there are already type hints for ensuring it is an array, meaning that it's fine to add the exception as a DX improvement. However, we probably should allow NULL as the empty value as well, since it's supported by \Drupal\block\BlockViewBuilder::preRender.

Good news: returning [] and NULL have exactly the same effect. We can file a follow-up to fix BlockViewBuilder which has been wrong this whole time. But let's not let it slow us here.

Converted the patch to an MR and added more tests.

Opened 📌 Fix BlockViewBuilder to handle NULL and [] Active per #23

Ran the test-only feature to show the coverage

Looking at the change don't see anything else pending. LGTM

Looks good, I wondered if we should add @throws to the method but it's not really an API method anyway and there's a @todo to remove it in one of the multiple follow-ups. Committed/pushed to 11.x, thanks!

catch → closed merge request !11049

Automatically closed - issue fixed for 2 weeks with no activity.