PHP is_null() Function

PHP is_null() checks whether a variable is NULL. It returns true only when the value is exactly NULL.

NULL is a special value in PHP that means “no value”. A variable becomes NULL when you assign NULL to it, or when a function has nothing to return.

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Syntax

is_null(mixed $value): bool

Parameters

Parameter	Description
value	Required. The variable or value you want to test

Return value: true if the value is NULL, otherwise false.

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Examples

Example #1: NULL, 0 and empty string

Only NULL gives true. Values like 0 and empty string are not NULL.

<?php
$a = null;
$b = 0;
$c = "";

var_dump(is_null($a));
var_dump(is_null($b));
var_dump(is_null($c));
?>

Output:

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Example #2: Use in if else

<?php
$result = null;

if (is_null($result)) {
    echo "Variable is NULL";
} else {
    echo "Variable is not NULL";
}
?>

Output:

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Example #3: Function returns NULL

Many functions return NULL when they do not find anything. Here our own function returns NULL if the user id is not 1.

<?php
function findUser($id) {
    return $id == 1 ? "Robin" : null;
}

$user = findUser(2);

if (is_null($user)) {
    echo "User not found";
} else {
    echo "Hello, " . $user;
}
?>

Output:

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Example #4: is_null() and === null

Both ways give same result. Using === null is a bit shorter, so some developers prefer it.

<?php
$a = null;

var_dump(is_null($a));
var_dump($a === null);
?>

Output:

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is_null() vs isset() vs empty()

Value	is_null()	isset()	empty()
NULL	true	false	true
0	false	true	true
“” (empty string)	false	true	true
“Hello”	false	true	false
Undefined variable	true (with warning)	false	true

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Summary

• is_null() returns true only for the NULL value.
• 0, “” and false are not NULL.
• It gives a warning for undefined variable, isset() does not.
• $var === null works same as is_null($var).

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