just a thought, not necessarily for this PR. Would it be sensible to throw an exception if any of the getter objects are still `NULL`? Ill be honest... I didn't really check what happens if `xios` getters fail. If `xios` throws the error anyway then it may not be necessary.
_Originally posted by @TomMelt in https://github.com/nextsimhub/nextsimdg/pull/555#discussion_r1607849575_