PHP is_null() Function – Check for Null Values in PHP Safely

Learn how to use the is_null() function in PHP to determine whether a variable is explicitly set to null, and why this matters in secure and reliable PHP applications.

Introduction – Why Use is_null() in PHP?

In PHP, variables can be unset, empty, false, or explicitly null — all of which behave differently. The is_null() function specifically checks whether a variable is exactly equal to null, which is useful when validating optional parameters, default values, or uninitialized data.

In this guide, you’ll learn:

• What null means in PHP
• How is_null() works with examples
• The difference between is_null(), isset(), and empty()
• When to use it in real-world PHP development

PHP is_null() Function

is_null(mixed $value): bool

The is_null() function returns true if the variable is null, and false otherwise.

Syntax and Example

$var = null;

if (is_null($var)) {
    echo "The variable is null.";
}

This check passes because $var is explicitly set to null.

Use Cases for is_null()

is_null() vs isset() vs empty()

Comparison Example:

$var = null;

var_dump(is_null($var)); // true
var_dump(isset($var));   // false
var_dump(empty($var));   // true

These differences are important when checking whether to process a value or default it.

Check for null in Arrays

$data = ['name' => null];

if (array_key_exists('name', $data) && is_null($data['name'])) {
    echo "Name is explicitly null.";
}

Useful for APIs or config arrays that may include null keys intentionally

Security Tip

is_null() is especially useful when checking authentication tokens, optional input, or query params where a missing value (isset) and a null value must be treated differently.

Summary – Recap & Next Steps

The is_null() function in PHP helps you identify variables that are explicitly set to null, which is vital in form processing, API handling, and security validation.

Key Takeaways:

• Use is_null() to check for explicitly null values
• It differs from isset() and empty() in behavior
• Helpful in API, DB, form, and optional param logic
• Combine with isset() for safe and complete checks

Real-World Use Cases:
Form validation, token verification, default value checks, DB column evaluation, handling nullable API responses

Frequently Asked Questions (FAQs)

What’s the difference between is_null() and isset()?
is_null() returns true if a variable is null; isset() returns false for both unset and null.

Is null the same as an empty string?
No. null !== ''. Use is_null() for null checks and empty() for falsy checks.

Can is_null() be used on unset variables?
No. You’ll get a notice. Use isset() first or suppress with @is_null().

How do I assign a variable to null?

$var = null;

Should I use is_null() when checking if an array key exists?
Yes, but use array_key_exists() first to avoid undefined index notices.