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.
Install
npx skills add dotnet/skills --skill migrate-nullable-referencesnpx skills add dotnet/skills --skill migrate-nullable-references -a claude-code -gnpx skills add dotnet/skills --skill migrate-nullable-references -a codex -ggemini skills install https://github.com/dotnet/skills.git --path plugins/dotnet-upgrade/skills/migrate-nullable-referencesgh skill install dotnet/skills migrate-nullable-referencesgit clone --depth 1 https://github.com/dotnet/skills /tmp/dotnet__skills
mkdir -p ~/.claude/skills ~/.agents/skills
cp -R /tmp/dotnet__skills/plugins/dotnet-upgrade/skills/migrate-nullable-references ~/.claude/skills/migrate-nullable-references # Claude Code
cp -R /tmp/dotnet__skills/plugins/dotnet-upgrade/skills/migrate-nullable-references ~/.agents/skills/migrate-nullable-references # Codex, Cursor, Gemini CLI, Copilot, OpenCode