Empty enumerable (Enumerable::EmptyError)

I'm not sure if this is an actual bug, or just a bad error, but this error happens if you pass in params to an operation and there's no permitted keys.

```
class SaveUser < User::SaveOperation
permit_columns :name
end
# user:beepbeep=true
SaveUser.create(params) do |_,_|
end
```

Will need to track down where this is happening.

Start with the SaveUser.create(params) example using params that contain no permitted keys, and capture the Enumerable::EmptyError stack trace. Trace the failure from the operation entry point to the empty-enumerable handling; done means the cause and expected behavior are established and the issue's error or behavior is addressed accordingly.

Written by the indexing model from the issue text.