Impossible to config override a key's value to an empty array

In order to overcome errors with overrides that already return `[]`, I had to change the override indicator to \EmptyIterator(). This is slightly less elegant but good enough and breaks no existing code. Tests are now passing.

Can the issue summary be updated with the modern template, to include the proposed solution please

Tested this a bit, unfortunately EmptyIterator is not supported everywhere, got:
TypeError: in_array(): Argument #2 ($haystack) must be of type array, EmptyIterator given in in_array() (line 123 of core/modules/user/src/Entity/Role.php). when saving permissions with overridden role config, it may occur on different occasions in different places as well if we map empty config this way, hard to tell really.

Ok, my mistake, haven't applied the patch properly, back to previous status.

Just got back from holiday so forgive the struggle. My previous comment vas valid after all, suggestion added.

Yes, good suggestion, Thats what I had locally but missed it when submitting the change in WebIDE.

Regarding the tests.. I think it just needs 2 more asserts that prove the config has actually been overridden to ['red', 'orange', 'yellow'] and [], however implemented.

Green.

Can a change record be written for this? Or docs be updated? This is a good example of an issue that a lot of devs would benefit from seeing.

I don't think there is a meaningful change so a change record is not applicable. I think there are release highlights but IMO this does not qualify. I think this qualifies as a routine bug fix for most devs.

Doing triage on the core RTBC queue → .

The issue summary is clear and has an proposed resolution which matches the MR. I do not see any unanswered questions in the comments and there are comments about the code in the MR.

I did not review the change or test it.

Leaving at RTBC.

We need to also add testing for this behaviour to \Drupal\Tests\Component\Utility\NestedArrayTest. The change seems like a good idea but I wonder if we need to change config overrider to find empty arrays and change them to \EmptyIterator objects because I think people would expect setting a config value in settings to an empty array to work.