Detecting insufficient PHP variables: FALSE vs NULL vs unset() vs empty()?

Question

What is the best way to define that a value does not exist in PHP, or is not sufficent for the applications needs.

$var = NULL, $var = array()

Answer 1

Another thing to remember is that since php is liberal in what it allows to evaluate to NULL or empty, it's necessary to use the identity operators (===, !== see http://php.net/operators.comparison. This is the reason why all of these comparison and equality functions exists, since you often have to differentiate between values with subtle differences.

If you are explicitly checking for NULL, always use $var === NULL