Required filter accepts empty objet

[TriPSs]

Describe the bug
When field is required in the filter an empty object is now enough.

Have you read the Contributing Guidelines?

Yes

To Reproduce
Steps to reproduce the behavior:

1. Set an field to be required in the filter
2. Example field foo is required, when sending { filter: { foo: {} } } is now accepted as valid

Expected behavior
Error to be thrown that a filter on foo is required