Adopt nullable reference types

The plan is to enable nullable reference types and review the nullability of all code (ie choose between nullable vs non-nullable references). A prerequisite for this is .NET 5 because of its improved unconstrained generics support.

In the process, we’ll likely want to make breaking changes to clarify the contract. For example IResourceContextProvider.GetResourceContext() today returns null when not found. Due to this loose contract, all callers are required to null-check or possibly face a NullReferenceException. So instead we’d like to offer ResourceContext GetResourceContext() (throws when not found) and ResourceContext? TryGetResourceContext (returns null when not found).

[bart-degreed]

Thanks for sharing your insights @dennisdoomen, greatly appreciated. As usual, there is no single right solution, so I’m going to choose on a case-by-case basis.

For our resource graph lookups, I believe Find* is the most appropriate fit.

[dennisdoomen]

I don’t know enough about your library to provide any specific advice, but I can provide generic advice about what I would expect:

• GetAttributeByPublicNameOrDefault - Makes total sense to me and aligns with LINQ’s API like FirstOrDefault.
• GetAttributeByPublicName - I would expect it to throw an exception if it can’t find the attribute by that public name
• FindAttributeByPublicName - I would expect it to return null if it can’t find the specified attribute
• TryGetAttributeByPublicName - This is a common convention. It would return false if it can’t find the specific attribute. It would return true if it can and pass the attribute through the out parameter. However, if the publicName parameter is null or empty, I would expect an ArgumentNullException or ArgumentException.