public void OrderByDescendingWithComparerSourceArgumentNull()
 {
     Assert.Throws <ArgumentNullException>(() => NullData.OrderByDescending(x => x, Comparer <object> .Default)).WithParameter("source");
 }
 public void OrderByDescendingSourceArgumentNull()
 {
     Assert.Throws <ArgumentNullException>(() => NullData.OrderByDescending(x => x)).WithParameter("source");
 }