CF6 - php8 - 0 Call to a member function get() on null

I have a form in CF6. I have to switch to php8 soon. I have
followed the instructions
https://www.chronoengine.com/faqs/76-chronoforms/5335-greyhead
But now I get the following error message:
0 Call to a member function get() on null

The problem was the plugin was fetching $this->_params->get('...', default) but _params was actually null for whatever reason.