using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var squares = ((IEnumerable<int>)null).Accumulate(x => x * x);

        Console.WriteLine("This is fine.");

    }

}

​

public static class AccumulateExtensions

{

    public static IEnumerable<U> Accumulate<T, U>(this IEnumerable<T> collection, Func<T, U> func)

    {

        foreach (var item in collection)

        {

            yield return func(item);

        }

    }

}