Rule is_null Replaces is_null($var) expression with null === $var. Warning Using this rule is risky Risky when the function is_null is overridden. Examples Example #1 --- Original +++ New <?php -$a = is_null($b); +$a = null === $b; Rule sets The rule is part of the following rule sets: @PhpCsFixer:risky @Symfony:risky Source class PhpCsFixer\Fixer\LanguageConstruct\IsNullFixer