This bug was reported by Douglas Kojetin <douglas dot kojetin at gmail dot com>, and was first
discussed in the post https://mail.gna.org/public/relax-users/2007-08/msg00008.html (Message-id:
<1E05882B-96B3-4875-B11B-0A6FEF423937@...>).
The fix was to simply test for the presence of the data structures. If these spin system specific
structures - 'model' and 'params' - were missing, then the bug will arise.
