Filter content-type with image via REST-Api


sorry for this simple question, but how can I query for content with an image via rest api?

I have a collection (cities) which has an an simple image-file in it:

"card_image": {
  "model": "file",
  "via": "related",
  "allowedTypes": [
  "plugin": "upload",
  "required": false

How can I query for these cities which have an card_image?

I tried something like http://localhost:1337/cities?card_image_null=false but I get an internal server error in this case.

Thanks for some help with this!

Best regards,