Error with thumb() method in File class for Virtual files

The CMS Questions
1

I’d like to switch one of my playground projects from Kirby 3 to 4 but get this error:

Whoops\Exception\ErrorException thrown with message "Declaration of CdnFile::thumb($options = null) must be compatible with Kirby\Cms\File::thumb(array|string|null $options = null): Kirby\Cms\FileVersion|Kirby\Cms\File|Kirby\Filesystem\Asset"

I am using a custom File class CdnFile according to this Cookbook:

...
public function thumb($options = null)
  {
    return $this;
  }
...

Any hints what iI need to change here?

Thank you!!

2

The signature has changed (type hint added), so you need to changes this in your method as well

3

Sorry, but how do I need to change it?

4 
public function thumb(array|string|null $options = null): Kirby\Cms\FileVersion|Kirby\Cms\File|Kirby\Filesystem\Asset) {}

Kirby 4 adds a lot of type hints where there were none in Kirby 3, so you will likely get some of these errors. If you extends a method in a child class (page model, file model etc.), then you need to make sure that the signatures of the methods match (number and type of arguments, return types).