Update scaffolders to support nullable reference types

Nullable reference types was a feature introduced in C# 8. In .NET 6 we intend to enable it for new projects by default (see dotnet/templating#3359).

Any code emitted into a project by scaffolders should ensure that it doesn’t introduce nullability warnings given the configuration of nullable reference types in the target project. This might mean updating the code to be “safe” for inclusion when nullable is on or off, or making the scaffolder emit different code depending on whether the project’s nullable context configuration (i.e. the value of the <Nullable> property in the .csproj file).

@vijayrkn

[deepchoudhery]

Hey @Rick-Anderson, all templates should be nullable friendly in .NET 7. There was a regression recently but should be resolved for GA.

[Rick-Anderson]

For Scaffolding the same templates are re-used for multiple TFM’s. So, the generated code is not nullable friendly for controllers, pages & identity. This is the current proposed plan of action:

Phase 1. The generated code from Scaffolding will add nullable disable at the page level to suppress the warning. Phase 2. Nullable enabled code will be scaffolded for all c# classes. Phase 3. Nullable enabled code will be scaffolded for Razor pages. Phase 4. Nullable enabled code will be scaffolded for Identity.

For .NET 7, I just needed to make the following change in 3 files

-  public Movie Movie { get; set; }
+ public Movie Movie { get; set; } = default!;

Can I get a guarantee this is fixed right for .NET 8? cc @vijayrkn @deepchoudhery