Question

Given the following C# code:

List<string> source = new List<string>();

IEnumerable<string> values = from value in source select value;

Will values ever be null or will it always return an empty sequence?

Answer 1

Yes it CAN return null if you have an extension method defined in your code somewhere like the following:

public static IEnumerable<string> Select(this List<string> list, Func<string, string> action)
{
    return null;
}

Otherwise no; it will return an empty sequence.