Display on ayarı nerede göremedim hocam

Fatal error: Uncaught Error: Call to undefined function sydney_slider_template() in /home2/savtek/public_html/wp-content/themes/sydney/header.php:60 Stack trace: #0 /home2/savtek/public_html/wp-includes/template.php(722): require_once() #1 /home2/savtek/public_html/wp-includes/template.php(671): load_template('/home2/savtek/p...', true) #2 /home2/savtek/public_html/wp-includes/general-template.php(41): locate_template(Array, true) #3 /home2/savtek/public_html/wp-content/themes/sydney/page-templates/page_front-page.php(6): get_header() #4 /home2/savtek/public_html/wp-includes/template-loader.php(98): include('/home2/savtek/p...') #5 /home2/savtek/public_html/wp-blog-header.php(19): require_once('/home2/savtek/p...') #6 /home2/savtek/public_html/index.php(17): require('/home2/savtek/p...') #7 {main} thrown in /home2/savtek/public_html/wp-content/themes/sydney/header.php on line 60

iki dediğinizi de yapınca bu hatayı alıyorum hocam
edit: tema null değil ancak bi sitede önüme null plugin denk gelmişti onu yükledim sanırım ondan oldu

edit 2: yalnızca wp debug ekleyince

Error thrown

Call to undefined function sydney_slider_template()

bunu alıyorum