Generic functions and value types

Do generic functions work well with nullable value types, or do they box behind the scenes?

For example I have a helper function like this:

public static TResult Return<TInput, TResult>(this TInput o, Func<TInput, TResult> evaluator, TResult failureValue)
    where TInput : class
{
    if (o == null) return failureValue;
    return evaluator(o);
}

Which I use to offer a fallback value when something is null, eg

var log = person.Return(p => p.log, emptylog)

So depending on whether log is a value or reference type, do I need a specialised version of Return() to handle value types without boxing, or is the above good for all cases?

EDIT: I'm curious as to why the author of this http://pastebin.com/vdS1uNu1 has specializations for class -> struct, class -> class, etc.