The following warning could appear on Spamassassin White list page -Plesk , Domains, domain.tld, Mail, email@example.com, Spam filter, White List tab:
Warning: Invalid argument supplied for foreach() in C:\Program
Files\SWsoft\Plesk\admin\plib\class.SpamAssassin.php on line 1357
Please download the following file
and place it to %plesk_dir%/admin/plib
Note: Please see how to install Plesk hotfixes properly.
%plesk_dir% is environment variable which points to Plesk installation folder. By default it is C:\Program Files\SWsoft\Plesk
%plesk_bin% is environment variable which points to Plesk binaries folder. By default it is C:\Program Files\SWsoft\Plesk\admin\bin