Code Smell 12 - Null

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


  • 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



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

Sample Code



Most Linters can show null usages and warn us.


  • Null


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

More info


Photo by Kurt Cotoaga on Unsplash

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

This article is part of the CodeSmell Series.

Apoorv Tyagi's photo

I always felt that there is a huge gap when it comes to articles on software engineering in general

With you, Matt Moll & Mario Cervera coming i am glad those gaps now has been filled :)

Mario Cervera's photo

Glad to hear this Apoorv! You can definitely expect more articles on Software Engineering coming from me 😉

Maxi Contieri's photo

Thank you Apoorv Tyagi!

More articles are coming!

Syed Fazle Rahman's photo

Wow. This is a great series, mcsee. These will definitely help devs become 10x better. 🍻 Keep them coming.