If you send an empty star list (no detected stars) to Astrometrynet via a PinPoint SolveAllSky(), you get back a really ugly red-herring error:
Submission #417983 failed to create job:
...e "process_submissions.py", line 471, in dosub
img = get_or_create_image(df)
File "process_submissions.py", line 526, in get_or_create_image
raise Exception('This file\'s type is not supported.')
Exception: This file's type is not supported.
