[12.x] Fix PHP 8.5 null-key deprecations

[IonBazan]

PHP 8.5 deprecates using null as array key (accessing, setting, as well as things like array_key_exists()):

Using null as an array offset or when calling array_key_exists() is now deprecated. Instead an empty string should be used. RFC: https://wiki.php.net/rfc/deprecations_php_8_5#deprecate_using_values_null_as_an_array_offset_and_when_calling_array_key_exists

I have personally encountered this deprecation in parseVerbosity() as usually it's set to null when calling $this->line('message'). Other places were discovered by running the test suite. Please note that most likely not all occurrences were found yet.

[shaedrich]

Do we want to consider null to be ''? If we have an array containing an item with '', it will be returned, when null is given, which can be unintentional.

[IonBazan]

Using null as key currently has the same behaviour (PHP 8.4):

> $arr[null] = 'test'
= "test"

> $arr
= [
    "" => "test",
  ]

> $arr['']
= "test"

When it comes to Collection and Arr, I'm a bit on the fence. We can either silently cast it to string for the users to keep things working as before, or let the deprecation be triggered and expect an userland logic change.

[shaedrich]

Thanks for the explanation 👍🏻

[donnysim]

I mean, TKey is defined as TKey of array-key which mean only int|string. If you pass a null value to that is your bug and should be fixed in your code. Arrays cannot have null as keys so what are we "fixing" here? If there are bugs related to it in the framework, it should preferably be fixed on usage, not on implementation.

[IonBazan]

@donnysim I agree, however this test suggests we could still use null:

framework/tests/Support/SupportCollectionTest.php

Lines 5544 to 5549 in 559976f

	#[DataProvider('collectionClassProvider')]
	public function testGetWithNullReturnsNull($collection)
	{
	$data = new $collection([1, 2, 3]);
	$this->assertNull($data->get(null));
	}

I could imagine many users having $collection->get($another->pluck('id')->first()) or similar which will require adding ?? '' in many places to prevent deprecations from occurring which makes it less "fluent".

I also noticed that getOrPut might have inconsistent behaviour when null is passed - depending whether an empty string key exists or not. That's because offsetSet contains a null check. Let me add a test to demonstrate it.