Nullable type
See also Null References - The Billion Dollar Mistake by Tony Hoare, Tony Hoare, Null (SQL), Null reference, Null pointer, Null pointer exception, Null-Safety
TLDR: A nullable type is a data type that explicitly allows the representation of null values, introduced to handle the absence of a value safely. This concept gained prominence with the introduction of nullable annotations in C Sharp 2.0 in 2005 and was later adopted by languages like Kotlin and Swift. Nullable types prevent runtime errors by enforcing null safety at the type level.
https://en.wikipedia.org/wiki/Nullable_type
In C Sharp, nullable types are denoted by a question mark (`?`) appended to the type, such as `int?`. This allows the variable to hold either a value or `null`. For example, `int? number = null;` is valid and avoids potential runtime exceptions. Similarly, Kotlin uses explicit nullable types with the syntax `Int?`, and the compiler enforces checks to ensure safe usage, such as requiring null checks before accessing properties or methods.
https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/nullable-types/
The introduction of nullable types significantly reduces null pointer exceptions, a common source of bugs in many programming languages. By explicitly distinguishing between nullable and non-nullable types, developers are encouraged to handle null values properly, either by providing default values or using safe call operators (`?.`) to prevent unsafe dereferencing.
https://kotlinlang.org/docs/null-safety.html
Adopting nullable types enhances code clarity and robustness, especially in large-scale projects. Tools like SonarQube and Pylint analyze code for nullability issues, helping teams maintain high-quality, error-free codebases. As more languages incorporate null safety into their core, nullable types have become a standard practice for reducing runtime errors and improving software reliability.
https://www.sonarsource.com/products/sonarqube/
Nullable type