Error: Call to a member function label() on null

Sounds at least major.
However, we have great passing test coverage.
How can we reproduce your situation.

Yeah there was a recent fix that we use label of entity reference fields to populate the summary.

That code doesn't check the interface while not all entities (for instance config targets) do not have a label. Also not sure if we properly check if the entity load succeeded in the field item. (Problem stale field items where entities could be deleted)
Needs a fix and better test coverage.

I can take a look.

It would probably help a lot if i get some more information, if someone has been thinking about this, when this can happen. Is having config targets the only situation?
I will test in the meantime.

if ($field_type = $value->getType() == 'entity_reference') {
if (!in_array($key, ['type', 'uid', 'revision_uid'])) {
$summary[] = $paragraphs_entity->get($key)->entity->label();
}
}

That code doesn't check the interface while not all entities (for instance config targets) do not have a label

There isn't really a way to check it, best we can do is a fallback for the ID. Not the problem here, it would just result in an empty string if there is no label.

Also not sure if we properly check if the entity load succeeded in the field item.

This however is exactly the problem. Check with if (...->entity) before calling a method on it.

To reproduce, just delete the entity we're using for testing this, then reload the edit form with it closed.

@Berdir thanks
There might be a better place for the test but didn't find any obvious space?

About the test, the code that added that also added tests: #2850788: Add test for collapsed user Paragraph summary, I would just expand on that.

@Berdir
Yea, makes sense. Wanted to avoid having to create paragraph type and configuring it but not that much extra code. Thanks again.

Committed with a comment. Thx.