String filtering custom fields for "not empty"

[MalteMagnussen]

https://demo.netbox.dev/static/docs/rest-api/filtering/#string-fields

How do I find every dcim/devices or dcim/inventory-items with any value in a specific custom field?

Right now I am fetching literally every single dcim/devices and then in my code filtering for a specific custom field not being null.

Can I use the string fields filtering in the rest api to only get the dcim/devices where X custom field is not none?