nullchecks

NullChecks are checks performed in code to ensure that a value is not null before it is used. They are a defensive programming practice intended to prevent null reference errors, such as null pointer exceptions, which can cause runtime crashes or undefined behavior. In many languages, dereferencing a null value is a typical error; explicit null checks act as gates at the boundaries of a function or at critical accesses.

Techniques for null checking vary by language. Common patterns include guard clauses that return or throw when the value is null, and early exits to avoid nested conditionals. Some languages provide optional types (Option/Maybe) that encode absence without using null. Other features include safe navigation or null-conditional operators (for example, a?.b in several languages) and utility methods like Objects.requireNonNull in Java. Static null safety is also used in languages like Kotlin, Swift, TypeScript (with strictNullChecks), and Rust, which help prevent nulls from propagating into code paths.

Issues and trade-offs: excessive null checking can clutter code and harm readability; inconsistent checks can still allow null dereferences. Overhead from redundant checks is usually small but can affect hot paths. Practical strategies include validating inputs at public API boundaries, using non-null types internally, and replacing null with option types or default values when possible.

See also: Optional, Maybe, Null pointer exception, Null safety, Contracts.