Augmenting the “null” class (image classification) with out-of-domain images?

Curious whether augmenting a “null” class using unrelated images is a good idea or not.

For example let’s say you are developing a model to classify bird species. There are 20 classes (species). You have a 21st class for “not a bird” but all of the images show trees or blue sky, in other words they’re not very varied and the usual augmentations like cropping and rotating can only do so much. You want to make sure that the model …

classification computervision image images null