Upgrade from 1.7.2 to 1.7.9 failed

I upgraded from v1.7.2 to v1.7.9 and now the admin page gets the following error:

Fatal error: Uncaught Error: Call to undefined function yourls_nonce_field() in /home/customer/www/21stsoft.com/public_html/r/includes/functions-html.php:193 Stack trace: #0 /home/customer/www/21stsoft.com/public_html/r/admin/index.php(310): yourls_html_addnew() #1 {main} thrown in /home/customer/www/21stsoft.com/public_html/r/includes/functions-html.php on line 193

Help! Any ideas?

This is covered in Github issues, search for “yourls_nonce_field”