Www - Undefinded variable

When browsed to www.example.com gives me the following error:

Notice: Undefined variable: prefix in /home/admin/domains/example.com/public_html/wp-content/themes/theme12/functions.php on line 3769

There is no any prefix variable and line 3769. I tried to change the theme name of the theme to “theme15” and still getting error for “theme12”.

Everything is working without www n url

Update: Delete all theme12 and theme15 files and the error still exist.

So annoying why shows me error for file that not exist