public static async Task FoldAsyncImplicit_NullValue_Throws(Func <int, int, Task <int> > folder)
        {
            var actual = await Record.ExceptionAsync(() => CollectionExtensions.FoldAsync(null, folder))
                         .ConfigureAwait(false);

            var ane = Assert.IsType <ArgumentNullException>(actual);

            Assert.Contains("collection", ane.Message, Ordinal);
        }