Suppress nullable warnings by assigning null with the null-forgiving operator

[Flash0ver]

class MyClass
{
    public string MyProperty { get; set; }
}

Warning CS8618 Non-nullable property MyProperty must contain a non-null value when exiting constructor. Consider declaring the property as nullable.

class MyClass
{
    public string MyProperty { get; set; } = default!;
}

We expect usage for "Data-Contract" / Serialization types, and also Microsoft.Extensions.Options types.

Alternative

Fix with C# Required Members (proposal)
See https://github.com/dotnet/csharplang/blob/main/proposals/required-members.md