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csharp-nullable-reference-types

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.

skills/csharp-nullable-reference-types/SKILL.md

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Repository last updated: Oct 28, 2026
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csharp Declared skill tag
nullable Declared skill tag
nrt Declared skill tag
code-quality Declared skill tag
api-design Declared skill tag
design Derived category

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SKILL.mdcore · 11,610 bytes
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nrt-migration-playbook-reference.mddoc · 15,004 bytes
nullable-attributes-reference.mddoc · 14,639 bytes

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# 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.