Suppressing Warnings in PHP

Let the variable $test be undefined. As you already know, the value of such a variable will be equal to null. However, an attempt to access this variable will result in a warning:

<?php
	var_dump($test); // will output null and a warning
?>

A warning will also be shown when trying to check the variable against null:

<?php
	if ($test !== null) {
		echo '+++';
	} else {
		echo '---';
	}
?>

However, a check using the isset command will not result in a warning - it will be automatically suppressed:

<?php
	if (isset($test)) {
		echo $test;
	} else {
		echo 'variable does not exist';
	}
?>