Unknown notice if page is displayed

Hello, i have a problem. I 'm using your plugin "Democracy - Poll", but lately my site shows me some bug. On the voting display pages, they write me:

Notice: Undefined offset: 2 in /data/web/virtuals/181045/virtual/www/domains/raider.cz/wp-content/plugins/democracy-poll/class-DemPoll.php on line 324

For example here:

https://raider.cz/hlasovani/

Of course - Notice writes user number, directory, website name, plugin name, etc ..
But I'm an amateur, I don't understand more.

Can you help me please?

Thank you very much and have a nice day!

Tom