Add nullable information to Subscriber ArgumentMetadata

[fritz-gerneth]

Not sure if to make this argument mandatory, would be a breaking change if this is considered public API. Do not like default here either though (no reasonable default value)

[DanielBadura]

Suggested change

	public readonly bool $allowsNull,
	public readonly bool $allowsNull = false,

The default should be false, as this is the current situation pre this patch. And yes, this is public api. We currently have only one class which is marked internal and thereby is not public api :D

[fritz-gerneth]

How about making it default null instead? The reason I opted against null is that this can be false information without means to detect this (not passed does not mean not nullable). Having it null would suggest 'unknown'. But that puts more burden on users to also check for null of course :)

[DanielBadura]

But what would the behaviour be, if $allowsNull is null? Either it supports nullable values (true) or not (false), i cannot thing of a third option here 🤔

[fritz-gerneth]

Behavior would be left to the recipient of the ArgumentMetadata. This class is only about the information we have, null meaning "we do not have it".

But since nullable arguments were not supported before:

• they probably were either not nullable before
• or if nullable, they were never called with null

So I do not really have a strong opinion about this either way :)

[DanielBadura]

I would go with false as the default value as this was not supported before it is imho the right choice.

[DanielBadura]

Thank you!