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