--- title: Internals of C# nullable reference types - Migrating to... description: This deep-dive explains how the C# compiler encodes nullable reference type (NRT) information into Intermediate Language via NullableContextAttribute and... canonical: https://daily.dev/posts/internals-of-c-nullable-reference-types---migrating-to-nullable-reference-types---part-2-ayjpvmckr twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Internals of C# nullable reference types - Migrating to nullable reference types - Part 2 | daily.dev og:description: This deep-dive explains how the C# compiler encodes nullable reference type (NRT) information into Intermediate Language via NullableContextAttribute and... og:url: https://daily.dev/posts/internals-of-c-nullable-reference-types---migrating-to-nullable-reference-types---part-2-ayjpvmckr og:image: https://api.daily.dev/og/posts/ayjPvmCkr.png og:image:alt: Internals of C# nullable reference types - Migrating to nullable reference types - Part 2 og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Internals of C# nullable reference types - Migrating to nullable reference types - Part 2 **[Maarten Balliauw](https://daily.dev/sources/maartenballiauw)** · 10 min read · 0 upvotes · 0 comments ## Summary This deep-dive explains how the C# compiler encodes nullable reference type (NRT) information into Intermediate Language via NullableContextAttribute and NullableAttribute, with disassembled IL examples showing how value 0/1/2 signal oblivious, not-annotated, or annotated contexts. It then covers the four nullable annotation context settings (disable, enable, warnings, annotations), how to configure them project-wide via the csproj Nullable property or per-file with #nullable directives, and discusses trade-offs of each setting as a starting point for migrating an existing codebase to NRT, concluding that warnings is a good gradual starting point while annotations alone is of limited use. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### How does the C# compiler represent nullable reference types in the compiled IL? The compiler emits NullableContextAttribute and NullableAttribute custom attributes with an 8-bit integer value: 0 means oblivious (pre-C#8 behavior), 1 means not annotated (non-nullable by default), and 2 means annotated (nullable by default, as if every reference type had a trailing ?). These attributes are applied at the method, parameter, or type level, and the compiler tries to emit as few of them as possible by setting a default context and only flagging exceptions. _Developers decoding IL metadata for nullable types can compare notes on daily.dev._ ### What is the difference between the enable, disable, warnings, and annotations nullable contexts in a C# project? disable makes the compiler behave like pre-C# 8.0 with no nullable reference type support and disallows using ? on reference types. enable turns on both null reference flow analysis and the ability to use ? annotations. warnings turns on flow analysis and shows warnings for potential null dereferences without enabling annotation syntax. annotations lets you use ? syntax but disables flow analysis warnings entirely. _Teams planning a nullable reference types migration can track C# tooling guidance on daily.dev._ ### What is a good strategy for migrating an existing large C# codebase to nullable reference types without being overwhelmed by warnings? Start with disable as the project default (or omit the Nullable property entirely) and incrementally add #nullable enable file by file as each file is migrated, avoiding a flood of warnings all at once. Alternatively, start with warnings as the default to get flow-analysis warnings on potential null dereferences without yet requiring annotation syntax, then promote files to enable once fixed, optionally setting WarningsAsErrors to Nullable to enforce addressing them. _Developers phasing in nullable reference types across legacy code can follow migration patterns like this on daily.dev._ ## Similar posts on daily.dev - [Taming the Billion Dollar Mistake: Maarten Balliauw's Guide to C\# Nullable Reference Types](https://daily.dev/posts/taming-the-billion-dollar-mistake-maarten-balliauw-s-guide-to-c-nullable-reference-types-dhuc5b5o7) · JetBrains · 5 upvotes · 0 comments - [What Actually Changed Inside the .NET 11 JIT Compiler — Daily DevOps & .NET](https://daily.dev/posts/what-actually-changed-inside-the-net-11-jit-compiler-daily-devops-net-s6qx7oe7d) · Daily DevOps & .NET · 27 upvotes · 4 comments - [Making Reflection Native AOT Safe in .NET 10: DynamicallyAccessedMembers Guide](https://daily.dev/posts/making-reflection-native-aot-safe-in-net-10-dynamicallyaccessedmembers-guide-xpy12bjep) · We Are .NET · 3 upvotes · 0 comments --- Tags: [#c#](https://daily.dev/tags/c#) [View this post on daily.dev](https://daily.dev/posts/internals-of-c-nullable-reference-types---migrating-to-nullable-reference-types---part-2-ayjpvmckr) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Internals of C# nullable reference types - Migrating to nullable reference types - Part 2","url":"https://daily.dev/posts/internals-of-c-nullable-reference-types---migrating-to-nullable-reference-types---part-2-ayjpvmckr","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/internals-of-c-nullable-reference-types---migrating-to-nullable-reference-types---part-2-ayjpvmckr"},"datePublished":"2026-10-04T13:04:12.097Z","dateModified":"2026-10-04T13:05:26.709Z","description":"This deep-dive explains how the C# compiler encodes nullable reference type (NRT) information into Intermediate Language via NullableContextAttribute and...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/d82e6ea50425e2c3d1c29bafb291ffbc?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/d82e6ea50425e2c3d1c29bafb291ffbc?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Maarten Balliauw","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Maarten Balliauw","logo":"https://media.daily.dev/image/upload/s--rOTg3VYO--/f_auto,q_auto/v1791119043/logos/maartenballiauw?_a=BAMAMicg0","url":"https://daily.dev/sources/maartenballiauw"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/internals-of-c-nullable-reference-types---migrating-to-nullable-reference-types---part-2-ayjpvmckr","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"c#","timeRequired":"PT10M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Maarten Balliauw","item":"https://daily.dev/sources/maartenballiauw"},{"@type":"ListItem","position":3,"name":"Internals of C# nullable reference types - Migrating to nullable reference types - Part 2"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/internals-of-c-nullable-reference-types---migrating-to-nullable-reference-types---part-2-ayjpvmckr#faq","mainEntity":[{"@type":"Question","name":"How does the C# compiler represent nullable reference types in the compiled IL?","acceptedAnswer":{"@type":"Answer","text":"The compiler emits NullableContextAttribute and NullableAttribute custom attributes with an 8-bit integer value: 0 means oblivious (pre-C#8 behavior), 1 means not annotated (non-nullable by default), and 2 means annotated (nullable by default, as if every reference type had a trailing ?). 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