Why Activator.CreateInstance(Type) returns nullable object?

[zlatanov]

I am trying to use the new C# 8 nullability feature in our new projects and while trying to fix some warnings in regard to Activator.CreateInstance, I found out that it returns nullable object.

But after I looked at the code to see in which case does it really return null because I thought it wasn't possible, it turns out it doesn't. See code:

runtime/src/libraries/System.Private.CoreLib/src/System/Activator.RuntimeType.cs

Lines 82 to 94 in 4f9ae42

	public static object? CreateInstance(Type type, bool nonPublic) =>
	CreateInstance(type, nonPublic, wrapExceptions: true);
	internal static object? CreateInstance(Type type, bool nonPublic, bool wrapExceptions)
	{
	if (type is null)
	throw new ArgumentNullException(nameof(type));
	if (type.UnderlyingSystemType is RuntimeType rt)
	return rt.CreateInstanceDefaultCtor(publicOnly: !nonPublic, skipCheckThis: false, fillCache: true, wrapExceptions: wrapExceptions);
	throw new ArgumentException(SR.Arg_MustBeType, nameof(type));
	}

Here is the signature of CreateInstanceDefaultCtor:

runtime/src/coreclr/src/System.Private.CoreLib/src/System/RuntimeType.CoreCLR.cs

Line 3980 in 4f9ae42

internal object CreateInstanceDefaultCtor(bool publicOnly, bool skipCheckThis, bool fillCache, bool wrapExceptions)

Is this something that can be fixed and the annotation to be correct, or is there an obscure case in other runtimes and implementations where Activator.CreateInstance(Type) could possibly return null?

[slang25]

Relevant discussion: dotnet/coreclr#23774 (comment)

[jkotas]

Submitted #674 to fix the annotations on the internal implementation details and add some comments.

[zlatanov]

Totally forgot about nullable value types and boxing. Now it makes sense.