Undefined index: QUERY_STRING php error causing site to slow down (Prestashop 1.7)

Question

Im getting this error and im not really great at coding. Can anyone point me in a direction in laymen terms if possible.

Really appreciate any help.

ContextErrorException in FrontController.php line 1715: Notice: Undefined index: QUERY_STRING

    in FrontController.php line 1715
    at ErrorHandler->handleError('8', 'Undefined index: QUERY_STRING', '/hermes/bosnaweb04a/b313/ipg.bennadauld10872/tins/classes/controller/FrontController.php', '1715', array('extraParams' => array('q' => 'Categories-Classic Size Bouquet Arrangements', 'page' => null), 'uriWithoutParams' => '/3-bouquets', 'url' => 'https://www.tinsflowershop.com/3-bouquets', 'params' => array())) in FrontController.php line 1715
    at FrontControllerCore->updateQueryString(array('q' => 'Categories-Classic Size Bouquet Arrangements', 'page' => null)) in ProductListingFrontController.php line 118
    at ProductListingFrontControllerCore->prepareFacetForTemplate(object(Facet))
    at array_map(array(object(CategoryController), 'prepareFacetForTemplate'), array(object(Facet), object(Facet), object(Facet), object(Facet), object(Facet), object(Facet))) in ProductListingFrontController.php line 149
    at ProductListingFrontControllerCore->renderFacets(object(ProductSearchResult)) in ProductListingFrontController.php line 341
    at ProductListingFrontControllerCore->getProductSearchVariables() in ProductListingFrontController.php line 539
    at ProductListingFrontControllerCore->doProductSearch('catalog/listing/category', array('entity' => 'category', 'id' => '3')) in CategoryController.php line 106
    at CategoryControllerCore->init() in Controller.php line 186
    at ControllerCore->run() in Dispatcher.php line 379
    at DispatcherCore->dispatch() in index.php line 28