Types
PHP Manual

NULL

The special NULL value represents a variable with no value. NULL is the only possible value of type null.

A variable is considered to be null if:

  • it has been assigned the constant NULL.

  • it has not been set to any value yet.

  • it has been unset.

Syntax

There is only one value of type null, and that is the case-insensitive constant NULL.

<?php
$var = NULL;       
?>

See also the functions is_null and unset.

Casting to NULL

Casting a variable to null using (unset) $var will not remove the variable or unset its value. It will only return a NULL value.