Silly little change, I know.. but I actually ran into a case where I accidentally passed a list of models in without *ing them. When that happens, we get a string formatting exception (not all arguments were formatted) instead of the useful "that ain't a model, kid" business.
Merge pull request #413 from phill-tornroth/patch-1

Silly little change, I know.. but I actually ran into a case where I acci