Bad line comment breaks merge request discussion

In gitlab EE I’m seeing a “Something went wrong while fetching comments. Please try again.” red banner. This banner appears after I send a merge request discussion creation with particular base_sha, start_sha, head_sha, old_path, new_path, position_type, new_line and old_line fields in an object under the key position of the top level JSON. I figure this is due to something malformed, like an incorrect sha but debugging with nil information is hard - can I get some pointers?

Ah, so if I remove old_path and old_line (which, by the way, I have) then it works and does not entirely break the comment rendering. Based on this I have two requests:

  1. Could we get good error messages for this endpoint and perhaps a 4xx type error message on the REST endpoint?
  2. Could we ignore comments that cause internal errors and render all other comments/discussions?