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csharp-nullable-reference-types

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Guidelines for introducing and using nullable reference types (NRT) and System.Diagnostics.CodeAnalysis nullable attributes in C# / .NET codebases. Covers the nullability model, flow analysis, the null-forgiving operator, API design rules, the full attribute catalog (AllowNull, DisallowNull, MaybeNull, NotNull, NotNullWhen, MaybeNullWhen, NotNullIfNotNull, MemberNotNull, MemberNotNullWhen, DoesNotReturn, DoesNotReturnIf), the C# 14 field keyword, incremental migration of legacy codebases, and a code-generation checklist.

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

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