⟩ What is NULL in PHP context?
NULL is a special type that only has one value: NULL. To give a variable the NULL value, simply assign it like this −
$my_var = NULL;
The special constant NULL is capitalized by convention, but actually it is case insensitive; you could just as well have typed −
$my_var = null;
A variable that has been assigned NULL has the following properties:
It evaluates to FALSE in a Boolean context.
It returns FALSE when tested with IsSet() function.