C# Nullable Reference Types

When to Use

• Introducing nullable reference types (NRT) into a codebase that has not yet adopted them
• Writing or refactoring C# code that uses T? / nullable annotations
• Annotating APIs with System.Diagnostics.CodeAnalysis nullable attributes
• Designing public/internal APIs where nullability contracts matter
• Wrapping unannotated or legacy APIs so downstream callers still benefit from NRT
• Reviewing code for correct null-state analysis, guard helpers, and the field keyword

Core Goals

• Prevent NullReferenceException at runtime by making null intent explicit in signatures.
• Express contracts the type system cannot represent directly using the official nullable attributes.
• Adopt NRT incrementally in legacy codebases without a big-bang rewrite.

Core Nullability Model