I need to create an image field with a default value, which must also be nullable on single content entities. Contrary to text fields or entity reference fields, I was unable to remove this default value on single content entities.
E.g. I can create a text field with default value "Lorem ipsum". On node creation, the field is prefilled with that text, but I can also delete that text and the field will stay empty.
But on image fields, there is no button/option to remove the default value at all. I can remove an override image, but not the default one. Even after uploading a non-default image, storing, and then removing that image again, the default value kicks in again.
How can I make the image field "nullable"?
Note that I can not use media entity references, because I must support SVG and those images also must not leak into the reuseable global media pool.