Fatal error: Uncaught Error: Call to a member function addMessage() on null in /home/shionacoin/public_html/sonaltextileonline.com/vendor/magento/framework/Message/Manager.php:146 Stack trace: #0 /home/shionacoin/public_html/sonaltextileonline.com/vendor/magento/framework/Message/Manager.php(177): Magento\Framework\Message\Manager->addMessage(Object(Magento\Framework\Message\Error), 'Offer / Sale Pr...') #1 /home/shionacoin/public_html/sonaltextileonline.com/app/code/Fox/Seo/Observer/DiscontinuedCategoryCheck.php(51): Magento\Framework\Message\Manager->addError(Object(Magento\Framework\Phrase), 'Offer / Sale Pr...') #2 /home/shionacoin/public_html/sonaltextileonline.com/vendor/magento/framework/Event/Invoker/InvokerDefault.php(88): Fox\Seo\Observer\DiscontinuedCategoryCheck->execute(Object(Magento\Framework\Event\Observer)) #3 /home/shionacoin/public_html/sonaltextileonline.com/vendor/magento/framework/Event/Invoker/InvokerDefault.php(74): Magento\Framework\Event\Invoker\InvokerDefault->_callObserverMethod(Object(Fox\Seo\ in /home/shionacoin/public_html/sonaltextileonline.com/vendor/magento/framework/Message/Manager.php on line 146