I had a problem when I updated the version of Wordpress to the 5.1
Theme: GratMag 1.0
Fatal error : Call to a member function hook() on null in /home/mhd-01/www.*.it/htdocs/wp-content/themes/GreatMag/header.php on line 6
The problem seems to hooks call into header.php
Any advices to solve, please?