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Short answer

Nullable reference types let you mark which references may be null. In a nullable-aware context the compiler warns when you dereference something that might be null. [S1][S2]

Points

• The goal is fewer NullReferenceExceptions. [S1]
• T vs T? are the same .NET type; the difference is static analysis. [S2]
• Enable the feature with <Nullable>enable</Nullable> or #nullable pragmas. [S1][S2]
• The null-forgiving operator and null warnings are optional language features. [S2]

Claims

• id: C1 claim: Nullable references aim to reduce NullReferenceException. source: S1 evidence: "minimize the chance your code throws System.NullReferenceException"
• id: C2 claim: You can express which references allow null. source: S1 evidence: "express which references are intended to allow null"
• id: C3 claim: T and T? are the same .NET type at runtime. source: S2 evidence: "a variable of type T? are the same .NET type"
• id: C4 claim: Null-forgiving and null warnings are optional features. source: S2 evidence: "null-forgiving operator are optional language features"

Sources

• [S1] Nullable reference types - C#. Microsoft Learn. https://learn.microsoft.com/en-us/dotnet/csharp/nullable-references . License: CC BY 4.0 (dotnet/docs). Accessed 2026-11-05.
• [S2] Nullable reference types. Microsoft Learn. https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/nullable-reference-types . License: CC BY 4.0 (dotnet/docs). Accessed 2026-11-05.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

Source notice: .NET documentation © Microsoft. Licensed under Creative Commons Attribution 4.0 International (https://github.com/dotnet/docs/blob/main/LICENSE).

@misc{iil_note_m8f4jqgd,
  author = {{iinventedlight}},
  title = {{C\# nullable reference types: string vs string?}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/csharp-nullable-reference-types/},
  note = {Permanent ID iil:note:m8f4jqgd. License: CC-BY-4.0.},
}

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