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, Null-Safety

TLDR: A null pointer is a pointer in programming that does not point to any valid memory location or object. This concept, introduced in early programming languages like C in the 1970s, serves as a way to indicate the absence of a value or reference. However, improper handling of null pointers can lead to null pointer exceptions, causing runtime errors or application crashes.

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

A null pointer is often used as a sentinel value to indicate “no object” or “no data” in scenarios like uninitialized variables or when an object is explicitly set to null. For example, in C, the `NULL` macro is used to represent a null pointer, while in Java or C Sharp, the keyword `null` serves the same purpose. Attempting to dereference a null pointer leads to undefined behavior in C and CPP or throws a runtime exception in managed languages like Java.

https://en.cppreference.com/w/cpp/utility/nullptr

Languages like Kotlin and Swift have addressed the challenges of null pointers by introducing null-safety features. In these languages, nullable and non-nullable types are explicitly defined, and the compiler enforces proper handling of null values. For instance, Kotlin's safe call operator (`?.`) prevents dereferencing nulls, significantly reducing the occurrence of null pointer issues.

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

To mitigate the risks associated with null pointers, developers use defensive programming practices, such as null checks, default initializations, and static analysis tools like SonarQube or FindBugs. These tools scan codebases to identify potential null pointer exceptions and provide recommendations for safer alternatives, ensuring robust and reliable software systems.

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 behavior. 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 "not applicable", "not known", and "future" values.

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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