# Migrate Nullable References

Enable nullable reference types in a C# project and systematically resolve all warnings.

- Repository: https://github.com/managedcode/dotnet-skills (500 stars)
- Category: Engineering
- License: MIT
- Last updated: 2026-10-29
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add managedcode/dotnet-skills --skill migrate-nullable-references -g -a claude-code -y`
Codex: `npx skills add managedcode/dotnet-skills --skill migrate-nullable-references -g -a codex -y`
Cursor: `npx skills add managedcode/dotnet-skills --skill migrate-nullable-references -g -a cursor -y`
Gemini CLI: `npx skills add managedcode/dotnet-skills --skill migrate-nullable-references -g -a gemini-cli -y`

## Description

Enable nullable reference types in a C# project and systematically resolve all warnings. USE FOR: adopting NRTs in existing codebases, file-by-file or project-wide migration, fixing CS8602/CS8618/CS86xx warnings, annotating APIs for nullability, cleaning up null-forgiving operators, upgrading dependencies with new nullable annotations. DO NOT USE FOR: projects already fully migrated with zero warnings (unless auditing suppressions), fixing a handful of nullable warnings in code that already has NRTs enabled, suppressing warnings without fixing them, C# 7.3 or earlier projects. INVOKES: Get-NullableReadiness.ps1 scanner script.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# Nullable Reference Migration

Enable C# nullable reference types (NRTs) in an existing codebase and systematically resolve all warnings. The outcome is a project (or solution) with `<Nullable>enable</Nullable>`, zero nullable warnings, and accurately annotated public API surfaces, giving both the compiler and consumers reliable nullability information.

## When to Use

- Enabling nullable reference types in an existing C# project or solution
- Systematically resolving CS86xx nullable warnings after enabling the feature
- Annotating a library's public API surface so consumers get accurate nullability information
- Upgrading a dependency that has added nullable annotations and new warnings appear
- Analyzing suppressions in a code base that has already enabled NRTs to determine whether they can be removed

## When Not to Use

- The project already has `<Nullable>enable</Nullable>` and zero warnings, the migration is done unless the user wants to re-examine suppressions with a view to removing unnecessary ones (see Step 6)
- The user only wants to suppress warnings without fixing them (recommend against this)
- The code targets C# 7.3 or earlier, which does not support nullable reference types

## Inputs

| Input | Required | Description |
|-------|----------|-------------|
| Project or solution path | Yes | The `.csproj`, `.sln`, or build entry point to migrate |
| Migration scope | No | `project-wide` (default) or `file-by-file`, controls the rollout strategy |
| Build command | No | How to build the project (e.g., `dotnet build`, `msbuild`, or a repo-specific build script). Detect from the repo if not provided |
| Test command | No | How to run tests (e.g., `dotnet test`, or a repo-specific test script). Detect from the repo if not provided |

## Workflow

The rest: https://github.com/managedcode/dotnet-skills/blob/HEAD/catalog/Platform/Official-DotNet-Upgrade/skills/migrate-nullable-references/SKILL.md