apply-type-fns should give better error message if type does not exist

[camsaul]

Right now it just throws confusing NullPointerException.

[marksto]

@camsaul it gives java.lang.IllegalArgumentException - No implementation of method: :types of protocol: #'toucan.models/IModel found for class: clojure.lang.PersistentArrayMap at the moment, which seems quite straightforward. Should this issue be closed then?