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<!DOCTYPE html> <html> <body> <?php $a = 0; echo "a is " . is_null($a) . "<br>"; $b = null; echo "b is " . is_null($b) . "<br>"; $c = "null"; echo "c is " . is_null($c) . "<br>"; $d = NULL; echo "d is " . is_null($d) . "<br>"; ?> </body> </html>