PHP NULL Value

Null is a special data type which can have only one value, which is itself. Which is to say, null is not only a data type, but also a keyword.

A variable of data type null is a variable that has no value assigned to it.

When a variable is created without a value, it is automatically assigned a value of null.

Example : 

<?php

$x="Hello world!";

$x=null;

var_dump($x);

?>