When awaiting null it should throw

awaiting_null_should_throw.cs

[Fact]
public async Task When_awaiting_null_it_should_throw()
{
    try
    {
        Task t1 = Task.Run(() => { /* do nothing */ });
        Task t2 = null;
        await Task.WhenAll(t1, t2);
        Assert.True(false, "Should have thrown before!");
    }
    catch (Exception ex)
    {
        Assert.IsType<ArgumentException>(ex);
    }
}