Programmers use Null as different flags. It can hint an absence, an undefined value, en error etc. Multiple semantics lead to coupling and errors.

Problems

• Coupling among the callers and the senders.

• Mismatch among the callers and the senders.

• If/Switch/Case Polluting.

• Null is not polymorphic with real objects. Hence Null Pointer Exception

• Null does not exist on real world. Thus it violates Bijection Principle

Solutions

• Avoid Null.

• Use NullObject pattern to avoid ifs.

• Use Optionals.

Exceptions

• APIs, Databases and external systems where NULL does exist.

Sample Code

Wrong

Right

Detection

Most Linters can show null usages and warn us.

Tags

• Null

Conclusion

• Null is the billion dollar mistake. Yet, most program languages support them and libraries suggest its usage.

More info

• Null: The Billion Dollar Mistake

Credits

Photo by Kurt Cotoaga on Unsplash

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I couldn't resist the temptation to put in a null reference, simply because it was so easy to implement. This has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years.

Tony Hoare

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This article is part of the CodeSmell Series.