Also the field becomes unavailable if you unpublish all documents with that field.
I have added a boolean field to my content type. When trying to query the API once the custom type has changed - it says
function at(..)] unexpected field 'my.events.isOnline' on line:1.
This makes we worried as we are erroring on content rather than on config, which means if the editors remove all content without the field our filters will fail.