Clarification regarding `image` entries

Hello, I have 2 questions about `image` entries that I cannot find the answer to in the specs:

1. What happens when an `image.uri` points to a file which is missing?
Does the GLTF asset file become invalid?
2. What happens when an `image` entry has neither a `uri` field nor a `bufferView` field?
[This chapter](https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html#images) seems to imply that at least one of them would be required but I could not find a place where it is explicitly stated.