Not all data structures are nullable or null reference is undesirable. In this case you can use the null object pattern https://en.wikipedia.org/wiki/Null_objec

Not all data structures are nullable or null reference is undesirable. In this case you can use the null object pattern https://en.wikipedia.org/wiki/Null_object_pattern#Description https://en.wikipedia.org/wiki/Null_object_pattern#Descriptio...