Okay, I found a solution:
if(!isset($options['show_upcoming']) || 'true' == $options['show_upcoming']) { // default is true
$elements[] = $this->upcoming_element();
}
if(isset($options['show_past']) && 'true' == $options['show_past']) { // default is false
$elements[] = $this->past_element();
In line 106, there’s missing a “!” before the “isset” and instead of “||” there’s “&&” – I’m not a coder, so I don’t know, what any of these signs mean, but I changed it and now it works.
I hope, this is helping someone!