if you define a property with type: [String] and you try to set e.g. `"string"` instead of `["string"]` the error is hard to understand. <img width="1798" alt="Screenshot 2019-09-25 at 17 25 21" src="https://user-images.githubusercontent.com/8471/65615554-d5c65700-dfb9-11e9-8094-c7e64867f5f8.png">