The problem is in ImageUtils#getImageFromUriSave (BTW - there is typo).
it tries to resolve image wrt current UI's theme, what is wrong. Should use theme of authentication UI, of edited endpoint.
The expected fix will need to include two parts:
resolve bugfix itself - resolving wrt of correct theme.
converter & tests update: invalid files should not be silently overwritten with empty values. We can block saving invalid values (and add validation on UI, so that invalid path is red, and blocks save).