Regarding 12345alex at gmx dot net's example:
I think you miss the identical equal documentation line from: http://php.net/manual/en/language.operators.comparison.php
$a == $b Equal TRUE if $a is equal to $b after type juggling.
$a === $b Identical TRUE if $a is equal to $b, and they are of the same type.
print array() === NULL ? "True" : "False";