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

My vote goes for unset(), because non existing variables should generate an notice when used.

Testing gets a bit more complicated, because isset() wil be false if the variable is "not existings" or null. (Language designflaw if you'd ask me)

You could use array_key_exists() for valiables in $GLOBALS, $_POST etc.
For class properties there is property_exists().