Call to a member function getMode() on null

Hmm.. Is there a config for that block that is named core.entity_view_display.block_content.YOUR_BLOCK_TYPE.default.yml? That's what _toolbar_plus_get_view_mode should fall back to.

You are correct, there is no config for the display of this block, there is no core.entity_view_display.block_content.starterkit_horizontal_line.default.yml

So the question is, do we modify toolbar_plus to fallback to 'default' if it cant get the config, or is 'illegal' and should it be impossible to have blocks without a display setting ? On our end, we could programmatically create a custom 'hr' field, add that to the Manage display of the block type and then I think the error would be solved.

Steps to reproduce:
- Visit admin/structure/block-content/add
- Give the new block type a label
- save it, dont add fields, dont change 'Manage display'
- add this block on a layoutbuilder page
- visit the page

This will result in an error. Is that what we want, so every developer is forced to have a display config of each block type ? Or should toolbar_plus handle this gracefully, by changing toolbar_plus.module line 97 into:
$cached_view_modes[$original_id] = $view_display ? $view_display->getMode() : 'default'; for example ?

Hmm, I'm not able to reproduce that error on Umami 🤔

Let's just add that change and see how it goes.

¯\_(ツ)_/¯