https://DevOpsCloud.io -- Cloud Monk Losang Jinpa, Ph.D., MCSE/MCT, GitOps DevOps Engineer

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/

Snippet from Wikipedia: Null pointer

In computing, a null pointer or null reference is a value saved for indicating that the pointer or reference does not refer to a valid object. Programs routinely use null pointers to represent conditions such as the end of a list of unknown length or the failure to perform some action; this use of null pointers can be compared to nullable types and to the Nothing value in an option type.

A null pointer should not be confused with an uninitialized pointer: a null pointer is guaranteed to compare unequal to any pointer that points to a valid object. However, in general, most languages do not offer such guarantee for uninitialized pointers. It might compare equal to other, valid pointers; or it might compare equal to null pointers. It might do both at different times; or the comparison might be undefined behaviour. Also, in languages offering such support, the correct use depends on the individual experience of each developer and linter tools. Even when used properly, null pointers are semantically incomplete, since they do not offer the possibility to express the difference between a "Not Applicable" value versus a "Not known" value or versus a "Future" value.

Because a null pointer does not point to a meaningful object, an attempt to access the data stored at that (invalid) memory location may cause a run-time error or immediate program crash. This is the null pointer error. It is one of the most common types of software weaknesses, and Tony Hoare, who introduced the concept, has referred to it as a "billion dollar mistake".

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