NULL

null means no value. It is the only value of the null type, and it is written null (case does not matter, but lowercase is the standard).

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<?php
$middleName = null;

var_dump($middleName);

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NULL

When a variable is null

A variable is null when:

1. You assign null to it.
2. You never gave it a value (PHP also gives a warning when you read it).
3. You called unset() on it.

A function that has nothing to return also gives null.

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<?php
function sayHi(): void
{
    echo "Hi\n";
}

$result = sayHi();
var_dump($result);

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Hi
NULL

Checking for null

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<?php
$value = null;

var_dump($value === null);
var_dump(is_null($value));
var_dump(isset($value));

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bool(true)
bool(true)
bool(false)

null is not 0 and not “”

These three look similar but mean different things.

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<?php
var_dump(null === 0);
var_dump(null === "");
var_dump(null == false);

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bool(false)
bool(false)
bool(true)

Loose comparison (==) treats null as equal to false, 0 and "". Strict comparison (===) does not. That is why professional PHP uses ===.

A default for null

The null coalescing operator ?? gives a fallback when a value is null or missing.

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<?php
$nickname = null;
echo $nickname ?? "No nickname";

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No nickname

More on that in Null Coalescing Operator.