This is_null() function is an inbuilt function in PHP which is used to find whether a variable is NULL or not. It returns True if the given variable is null, otherwise return False.
bool is_null( $var )
$x === null
It is an identical comparison operator and it returns true if the value of $x is equal to NULL. Null is a special data type in PHP which can have only one value that is NULL. A variable of data type NULL is a variable that has no value assigned to it. Any variable can be empty by setting the value NULL to the variable.
$var === null