Nullptr in Json::Generic output

[Justin F]

In Put::GenericIterable there are two unguarded dereferences of field.second that can result in reads from nullptrs/uncaught exceptions

[Justin F]

This bug has apparently been present since generics were introduced: 919607f#diff-362a45ce75c777b60c17474e1860c696e2bab52d0f2e8b6190377594f4a878acR1243 will need to ensure unit tests more thoroughly cover nulls in json generic I/O.

[Justin F]

Fixed by f1bbfa6 , though more to go on object mapping before this can be merged

[Justin F]

Fixed as of #75