Fix for enforcement of required input fields

In some cases, Kraken was not correctly validating that required input fields were provided. This could result in an obtuse KT-CT-7899 "internal error occurred" error response, rather than the more helpful validation error that should have been returned. This is in the process of being corrected, so API callers should see more helpful validation errors in the near future, specifying which required fields are missing. This will result in the error code being returned in these cases changing from KT-CT-7899 to a mutation-specific error code.