using System;

using System.Threading.Tasks;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var l = new List<string>();

        var noWarning = M1(x => Task.FromResult<IEnumerable<string>>(l));

        var hasWarning = M1(async x => l);

    }

    static string M1(Func<int, Task<IEnumerable<string>>> getList) 

    {

        return "";

    }

}