Null & Null-Safe Operators

Missing data is everywhere — absent array keys, unset properties, optional objects. PHP gives you three sharp tools for handling null gracefully: ?? for defaults, ??= for lazy assignment, and ?-> for safe object chains.

Learn Null & Null-Safe Operators in our free PHP course — a beginner-friendly interactive lesson with worked examples, a practice exercise and a quick recall.

Part of the free Php course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

What You'll Learn in This Lesson

1️⃣ What null Really Is

null is the type that means "no value". A variable is null when you assign null , when a function returns nothing, or when you read an array key or property that doesn't exist. Test for it with === null or is_null() — and don't confuse "is null" with "is falsy": 0 and "" are falsy but are not null.

2️⃣ The ?? Operator

The null coalescing operator ?? returns the left side unless it's null or undefined, in which case it returns the right side — and it never emits an "undefined key" warning. It also chains , walking left to right until it finds a non-null value.

3️⃣ The ??= Operator

The null coalescing assignment operator ??= writes a value only if the target is currently null or unset. It's the tidy shorthand for "set this default if nothing's there yet", and it's great for lazy initialisation and caching.

4️⃣ ?? vs ?: — Null vs Falsy

This is the distinction that trips people up. ?? only reacts to null ; the short ternary ?: (the "Elvis" operator) reacts to anything falsy . For a value of 0 or "" , the two behave completely differently — choose deliberately.

5️⃣ The Nullsafe Operator ?->

Added in PHP 8, the nullsafe operator ?-> reads a property or calls a method only if the object isn't null; if it is, the whole chain evaluates to null instead of throwing. It replaces piles of nested isset() checks for optional object graphs, and pairs perfectly with ?? for a final default.

Now you try. Fill the ___ blanks with ?? or ??= .

🧩 Reorder Challenge

These scrambled lines should pick a display name and default a role. Put them in the order that prints Sam (member) .

Create the array first, then derive $name and $role from it, then echo. The chain $user['nick'] ?? $user['name'] skips the null nickname and lands on "Sam", and the missing role key falls back to "member". Output: Sam (member) .

🧠 Quick Recall

Predict the output before revealing each answer.

Prints 0 . ?? only replaces null, and 0 is not null. With ?: instead, it would print none .

Prints 5 . The first ??= sets $x to 5 because it was null; the second is skipped because $x is no longer null.

Evaluates to n/a . The ?-> short-circuits the null object to null (no error), then ?? supplies the default.

Common Errors (and the fix)

• A value of 0 gets replaced by your default — you used ?: when you meant ?? . Use ?? to react only to null.
• "Attempt to read property on null" — you chained -> on a possibly-null object. Use ?-> .
• "Undefined array key" still warns — you only guarded part of the access. The whole expression on the left of ?? is protected, so write $a['x']['y'] ?? null .
• You can't write $obj?->prop = 1 — nullsafe is read-only; you cannot assign through it.

Pro Tips

• 💡 Reach for ?? on every optional read. It both defaults and silences the missing-key warning.
• 💡 Remember: ?? = null, ?: = falsy. The difference matters most around 0 and "" .
• 💡 Combine ?-> with ?? for clean optional chains: $a?->b?->c ?? 'default' .

📋 Quick Reference — Null Operators

Operator

Reacts to

Example → result

??

null / undefined

$x ?? 'd'

??=

$x ??= 'd'

?:

any falsy value

$x ?: 'd'

?->

null object

$o?->m()

=== null

exactly null

$x === null

is_null()

is_null($x)

Frequently Asked Questions

Mini-Challenge: Build a Greeting

Write it yourself, run it on onecompiler.com/php or your own machine, then check against the expected output in the comments.

🎉 Lesson Complete!

• ✅ null means "no value"; test with === null
• ✅ ?? defaults null/undefined values without warnings and chains left to right
• ✅ ??= assigns only when the target is null/unset
• ✅ ?? reacts to null; ?: reacts to falsy — they differ at 0 and ""
• ✅ ?-> safely traverses possibly-null objects
• ✅ Next lesson: Checkpoint — combine everything you've learned in PHP Basics

Practice quiz

Continue this course

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• Next: Checkpoint: PHP Basics