Nullable reference types
Nullable reference types are a C# compiler feature that annotates reference types and performs compile-time analysis of possible null values.
.NET in Action, Second Edition
A nullable reference type is a C# type annotation that allows a reference to represent null and participates in compile-time nullability analysis.
- How it is used
- Marks properties and method results that may be null so compiler warnings can guide application code.
- How deep it goes
- Explains annotations, project configuration, warnings, and modeling choices through working examples; stops short of compiler-analysis internals.
- Examples
- Uses an options property, a book-title constructor, and a nullable comic lookup to expose different reasons for nullability.
- What you can do after
- Apply it via C# annotations and project settings to address warnings without permitting null where a value is required.
Read how .NET in Action, Second Edition explains nullable reference types →
ASP.NET Core in Action, 3e
Nullable reference types are a C# compiler feature that represents and checks whether reference-type values may be null.
- How it is used
- Uses nullable annotations to align minimal API handler parameters with missing or null request values.
- How deep it goes
- Explains annotations, project enablement, binding behavior, and analyzer warnings, but does not descend into compiler implementation.
- Examples
- Demonstrates Product?, nullable route and query parameters, and a net7.0 project file with Nullable enabled.
- What you can do after
- Apply nullable annotations and compiler or IDE warnings to configure safer optional parameters in minimal API endpoints.
Read how ASP.NET Core in Action, 3e explains nullable reference types →
Related concepts
- optional function argumentuses · An optional function argument is an input corresponding to a parameter that a caller is not required to supply because omission is permitted by the function's interface.
- missing valueaddresses · A missing value is a marker or condition indicating that an expected data value or reference is absent, unavailable, unknown, or inapplicable.
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