Unable to parse a contract with a raw object

In a DTO modeling an error, we have parameters in it, used to format error message to user for instance.

As this parameter can be a number, a string or whatever, we have something like this in our contract :

```
components:
schemas:
Problem:
type: object
properties:
title:
type: string
params:
type: object
additionalProperties:
type: object
```

But the generator is unable to narrow a Type for params values. A workaround has been to add a `format: json` on `additionalProperties` in our contract but it is not a viable solution on the long term. It eventually allows to generate correctly our other clients, but this is not what we want to see here.