Nullability Attributes in Older Projects In order to actually use these attributes, they need to be defined. If you are using .NET Standard 2.1 or .NET Core 3.0, that’s already done for you.

This report is a case study on upgrading a C# 7 class library to C# 8 with nullable reference types. The project used is a collection of MVVM base classes, reflection code, and utility functions.