Make type parameter T of the Null() method nullable and add overload for value types.

[amal-stack]

• Solves Make T nullable #260 which suppresses nullable warnings.
• Adds an additional overload of Null() with a value type constraint on T (where T : struct) to allow assignment to non-nullable value types when passed nullable value types (Enhanced support for value types #242) . For example, the following is now allowed with this overload:

int? nullableInt = 42;
int nonNullableInt = Guard.Against.Null(nullableInt, nameof(nullableInt));

• Also added unit tests to ensure that the type of the return value is non-nullable.

[mwasson74]

Hey @amal-stack, me again from #258. I see you've submitted this PR. Do you know when this might be released? I see it's still "open" and says something about "Expected - Waiting for status to be reported" but I have no idea what that means 😬

[mwasson74]

Hey @amal-stack, me again. Sorry to keep bothering you, but it seems this got "stuck" again. Any idea when this will be merged and released?