Menu Error Code

I have this error code on the wordpress website I am creating, which means I cannot access the menu to make changes. Does anyone know what this is or how I resolve it?

Fatal error : Uncaught Error: Attempt to assign property “front_or_home” on null in /homepages/7/d70646224/htdocs/clickandbuilds/NewMissionWebsite/wp-admin/includes/nav-menu.php:379 Stack trace: #0 /homepages/7/d70646224/htdocs/clickandbuilds/NewMissionWebsite/wp-admin/includes/template.php(1522): wp_nav_menu_item_post_type_meta_box(NULL, Array) #1 /homepages/7/d70646224/htdocs/clickandbuilds/NewMissionWebsite/wp-admin/nav-menus.php(945): do_accordion_sections(Object(WP_Screen), ‘side’, NULL) #2 {main} thrown in /homepages/7/d70646224/htdocs/clickandbuilds/NewMissionWebsite/wp-admin/includes/nav-menu.php on line 379

Hi, You can go to ask item support section. Then theme author help you.