The special NULL value represents that a variable has no value. NULL is the only possible value of type NULL.
Note: The null type was introduced in PHP 4.
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().
There is only one value of type NULL, and that is the case-insensitive keyword NULL.
<?php$var = NULL; ?>
See also is_null() and unset().
