In this article we describe what Nullable reference types is.
From Umbraco version 10, Nullable Reference Types is enabled by default in Umbraco.
Nullable reference types is a group of features introduced in C# 8.0. These features can be used to minimize the likelihood that your code causes the runtime to throw System.NullReferenceException.
Nullable reference types includes three features that help you avoid these exceptions, including the ability to explicitly mark a reference type as nullable:
Improved static flow analysis that determines if a variable may be null before dereferencing it.
Attributes that annotate APIs so that the flow analysis determines null-state.
Variable annotations that developers use to explicitly declare the intended null-state for a variable.
To learn more about Nullable Reference Types, refer to the Microsoft Documentation