walshjupes

NullReferenceException means that you are trying to use a reference variable whose value is Nothing/null . When the value is Nothing/null for the reference variable, which means that it is not actually holding a reference to an instance of any object that exists on the heap. string str = null; str.ToUpper(); Above c# code throws a NullReferenceException at the second line because you can't call the instance method ToUpper() on a string reference pointing to null. So, check your code once again.