See also Null References - The Billion Dollar Mistake by Tony Hoare, Tony Hoare, Null (SQL), Null reference, Null pointer, Null pointer exception, Nullable type, Null-Safety

TLDR: A null reference occurs when a pointer or variable does not point to any valid object or memory location, often resulting in runtime errors. Introduced with the development of early programming languages like ALGOL in the 1960s, null references are a common source of bugs and application crashes in languages such as Java, CPP, and C Sharp.

https://en.wikipedia.org/wiki/Null_pointer

Null references are used to indicate the absence of a value or object, but dereferencing them (e.g., attempting to access properties or methods) without proper checks results in null pointer exceptions. For example, in Java, calling a method on an uninitialized object reference will throw a `NullPointerException`. Best practices, like performing null checks or using modern constructs like the Optional class, mitigate these issues.

https://docs.oracle.com/javase/8/docs/api/java/util/Optional.html

Modern programming languages, such as Kotlin and Swift, introduced in 2011 and 2014 respectively, aim to eliminate null reference issues through nullable and non-nullable type annotations. These languages enforce explicit handling of nullable values at compile time, reducing the likelihood of runtime errors caused by null references. This approach significantly improves code safety and reliability.

https://kotlinlang.org/docs/null-safety.html

To handle null references effectively in legacy systems, developers often rely on defensive programming practices like using default values, safe navigation operators (e.g., `?.` in C Sharp), and static analysis tools such as FindBugs or SonarQube. These tools analyze codebases to identify potential null dereferencing, ensuring more robust and maintainable software.

https://www.sonarsource.com/products/sonarqube/

Null reference