Hmm, one issue is that a request e.g. for "Ag" dos data currently tries to collect such data for all Ag polymorphs and produces an error if any of them fail. This is unfortunate, and I'll see what we can do to make this behave better, e.g. yield a list with dos data for polymorphs that have it and an error message for those that don't.
In the meantime, if you use an MP material id in the request, e.g.
for our most thermodynamically stable Ag polymorph, you will see dos data.
The 'NoneType' error, for the case of fetching dos and bandstructure data, is indeed just given if data is unavailable. I just changed things so that the more readable error is given. There is more to do about this, though, as I mentioned above, and I'll post back here when that's done.
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