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

Problems 😔

• Coupling between callers and 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 😃

1. Avoid Null.
2. Use the NullObject pattern to avoid ifs.
3. Use Optionals.

https://hackernoon.com/null-the-billion-dollar-mistake-8t5z32d6?embedable=true

Refactorings ⚙️

https://hackernoon.com/code-refactoring-tips-no-015-remove-null?embedable=true

https://hackernoon.com/refactoring-029-how-to-replace-null-with-collection?embedable=true

https://hackernoon.com/refactoring-014-how-to-remove-if?embedable=true

Context 💬

When you use null, you encode multiple meanings into a single value.

Sometimes you want to represent an absence.

Sometimes you mean you have not loaded your objects yet.

Sometimes you mean error.

Callers must guess your intent and add conditionals to protect themselves.

You spread knowledge about internal states across your codebase.

Sample Code 📖

Wrong 🚫

class CartItem { constructor(price) { this.price = price; } } class DiscountCoupon { constructor(rate) { this.rate = rate; } } class Cart { constructor(selecteditems, discountCoupon) { this.items = selecteditems; this.discountCoupon = discountCoupon; } subtotal() { return this.items.reduce((previous, current) => previous + current.price, 0); } total() { if (this.discountCoupon == null) return this.subtotal(); else return this.subtotal() * (1 - this.discountCoupon.rate); } } cart = new Cart([ new CartItem(1), new CartItem(2), new CartItem(7) ], new DiscountCoupon(0.15)]); // 10 - 1.5 = 8.5 cart = new Cart([ new CartItem(1), new CartItem(2), new CartItem(7) ], null); // 10 - null = 10

Right 👉

class CartItem { constructor(price) { this.price = price; } } class DiscountCoupon { constructor(rate) { this.rate = rate; } discount(subtotal) { return subtotal * (1 - this.rate); } } class NullCoupon { discount(subtotal) { return subtotal; } } class Cart { constructor(selecteditems, discountCoupon) { this.items = selecteditems; this.discountCoupon = discountCoupon; } subtotal() { return this.items.reduce( (previous, current) => previous + current.price, 0); } total() { return this.discountCoupon.discount(this.subtotal()); } } cart = new Cart([ new CartItem(1), new CartItem(2), new CartItem(7) ], new DiscountCoupon(0.15)); // 10 - 1.5 = 8.5 cart = new Cart([ new CartItem(1), new CartItem(2), new CartItem(7) ], new NullCoupon()); // 10 - nullObject = 10

Detection 🔍

Most Linters can flag null usages and warn you.

Exceptions 🛑

You sometimes need to deal with null when you integrate with databases, legacy APIs, or external protocols.

You must contain null at the boundaries and convert it immediately into meaningful objects.

Tags 🏷️

• Null

Level 🔋

[x] Intermediate

Why the Bijection Is Important 🗺️

When you use null, you break the bijection between your code and the MAPPER.

Nothing in the mapper behaves like null.

Absence, emptiness, and failure mean different things.

When you collapse them into null, you force your program to guess reality and you invite defects.

AI Generation 🤖

AI generators often introduce this smell.

They default to null when they lack context or want to keep examples short and also because it is widespread (but harmful) industry default.

AI Detection 🧲

You can instruct AI to remove nulls with simple rules.

When you ask for explicit domain objects and forbid nullable returns, generators usually fix the smell correctly.

Try Them! 🛠

Remember: AI Assistants make lots of mistakes

Without Proper Instructions 📵

• ChatGPT
• Claude
• Perplexity
• Copilot
• You
• Gemini
• DeepSeek
• Meta AI
• Grok
• Qwen

With Specific Instructions 👩‍🏫

• ChatGPT
• Claude
• Perplexity
• Copilot
• You
• Gemini
• DeepSeek
• Meta AI
• Grok
• Qwen

Conclusion 🏁

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

Relations 👩‍❤️‍💋‍👨

https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xviii

https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxxii

https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xix

https://hackernoon.com/how-to-get-rid-of-annoying-ifs-forever-zuh3zlo

https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-viii-8mn3352

https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxx

https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xliii

https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxxix

https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxvi

https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xlii

https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxxii

https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xx-we-have-reached-100

https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-ix-7rr33ol

https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-v-evj3zs9

More Information 📕

https://hackernoon.com/null-the-billion-dollar-mistake-8t5z32d6?embedable=true

Credits 🙏

Photo by Kurt Cotoaga on Unsplash

Tony Hoare

https://hackernoon.com/400-thought-provoking-software-engineering-quotes?embedable=true

This article is part of the CodeSmell Series.

https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-i-xqz3evd?embedable=true

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