​​NullReferenceException in C# (part 1)

The NullReferenceException is an exception that will be thrown while accessing a null object.

The following example shows the code that throws the NullReferenceException:

In the above example, a NullReferenceException will be thrown in the DisplayCities() function while accessing cities list using a foreach loop because the cities list is null. If the caller of the DisplayCities() function pass a null IList value then it will raise a NullReferenceException.