Warning message after software update server

My provider updated the software on the server and now I get this warning message (see below) on my website (on top of it) but it works fine for the rest. I need to say that I didn’t update the theme for a long time because I made some changes (in the code) to several parts of it and an update would destroy all that work (unfortunately I don’t remember what changes I made and where). What could be the problem?

Warning: Creating default object from empty value in /home/XXXX.nl/www/Wordpress/wp-content/themes/hatch/library/functions/core.php on line 32