misc bugfixes (empty collections, collection filters)

- [ ] test coverage
- [x] finished the code
- [x] gathered feedback for my changes
- [ ] submited changes to the documentation


| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| Tests pass?   | none
| Fixed tickets | none
| Doc           | https://github.com/massiveart/husky-validation/issues/29