using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var list = GetEmptyList();

        var value = list.FirstOrDefault()?.FirstOrDefault().Prop1;

        Console.WriteLine(value);

        Console.WriteLine(value == null);

        var list2 = GetNull();

        var value2 = list.FirstOrDefault()?.FirstOrDefault().Prop1;

        Console.WriteLine(value2);

        Console.WriteLine(value2 == null);

    }

    private static IEnumerable<IReadOnlyCollection<Test>> GetEmptyList()

    {

        return Array.Empty<IReadOnlyCollection<Test>>();

    }

    private static IEnumerable<IReadOnlyCollection<Test>> GetNull()

    {

        return null;

    }

}

​

struct Test

{

    public string Prop1 { get; set; }

}