diff --git a/src/Validator.php b/src/Validator.php
index e7efac4..0bdc3ae 100644
--- a/src/Validator.php
+++ b/src/Validator.php
@@ -43,7 +43,7 @@ public static function validateMinMaxTol($begin, $end, $tol) {
     }
 
     public static function validateWidths($widths) {
-        if ($widths == NULL) {
+        if (is_null($widths)) {
             throw new \InvalidArgumentException("`widths` array cannot be `null`");
         }