Testing for 'lazy loaded' null IEnumerable in c#?

Question

I've simplified a piece of a deferred execution code, but how on earth do you check the following is not null/empty without wrapping it in a try/catch?

    string[] nullCollection = null;
    IEnumerable<string> ienumerable = new[] { nullCollection }.SelectMany(a => a);

    bool isnull = ienumerable == null; //returns false
    bool isany = ienumerable.Any(); //throws an exception

Answer 1

You just need to make your lambda more resilient to null entries:

IEnumerable<string> ienumerable = new[] { nullCollection }
    .SelectMany(a => a ?? Enumerable.Empty<string>());

bool isany = ienumerable.Any(); // Sets isany to 'false'

Answer 2

You cannot do that, because that's the same as asking "how can I tell that method will not throw NullReferenceException without invoking it?". Having no other clues the only way is actually invoke such methods and observe the result. Enumerating IEnumerable is just invoking bunch of MoveNext calls on it's enumerator, and any such call might throw any exceptions.