Enable nullable in project

[Arthurvdv]

Enabling nullable reference types will improve the LinterCop on reducing possible System.NullReferenceException errors.

New rules will automatically have the nullable reference types enabled, where existing rules will be reviewed in the future.

Originally, all reference-type variables were nullable. This meant that you always had to consider the possibility of a null reference and code accordingly. If it was your intention that a variable never be null, there was no way to enforce that. If you treated it like it would never be null, there was always the possibility of a NullReferenceException at run time if someone mistakenly set it to null.

Now, you can specify which variables should be nullable and which shouldn't and the compiler will enforce that. If you try to make a non-nullable variable null, a compiler error will prevent that. If you treat a nullable variable as though it definitely won't be null, a compiler warning will alert you.

https://stackoverflow.com/a/74583086