The null type is PHP's unit type, i.e. it has only one value: null.

Undefined, and unset() variables will resolve to the value null.


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


Casting to null


This feature has been DEPRECATED as of PHP 7.2.0, and REMOVED as of PHP 8.0.0. Relying on this feature is highly discouraged.

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

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