[C#] I wish I knew : Nullable<T>.GetDefaultValue(T)

I've been a professional C# developer for years now, but I'm still discovering trivial stuffs. In "I wish I knew", I describe a feature that I missed.

Given the following:

struct T {}

T? nullable;
T fallback;

I always though the only alternative to this:

T value = nullable.HasValue ? nullable.Value : fallback;

was this:

T value = nullabe ?? fallback;

But it turns out, you can also do this:

T value = nullabe.GetValueOrDefault(fallback);

Well... I'm not sure I'm really gonna use it but it made me realize how much I wish these LINQ extension methods exist:

ElementAtOrDefault<TSource>(this IEnumerable<TSource> source, TSource fallback);
FirstOrDefault<TSource>(this IEnumerable<TSource> source, TSource fallback);
LastOrDefault<TSource>(this IEnumerable<TSource> source, TSource fallback);
SingleOrDefault<TSource>(this IEnumerable<TSource> source, TSource fallback);