Update DefaultValidator.php

Author: Stanislav Idolov

app/code/Magento/Catalog/Model/Product/Option/Validator/DefaultValidator.php

@@ -108,7 +108,7 @@ protected function isValidOptionTitle($title, $storeId)
         }
 
         // checking whether title is null and also changed is_empty to is_null
-        if ($this->isNull($title)) {
+        if ($title === null) {
             return false;
         }
 
@@ -170,15 +170,4 @@ protected function isNegative($value)
     {
         return intval($value) < 0;
     }
-
-    /**
-     * check whether title is null
-     *
-     * @param $title
-     * @return bool
-     */
-    protected function isNull($title)
-    {
-        return is_null($title);
-    }
 }