public static MonadOr <TResult> Join <TSource, TInner, TKey, TResult>(
this MonadOr <TSource> @this,
MonadOr <TInner> inner,
Func <TSource, TKey> outerKeySelector,
Func <TInner, TKey> innerKeySelector,
Func <TSource, TInner, TResult> resultSelector)
=> @this.Join(
inner,
outerKeySelector,
innerKeySelector,
resultSelector,
null);
