Restful webservice testing e2e

I have a slight overview of testing webservices with restassured. Can someone please tell if what will be the output response and code while testing restful webservice if we: 1. Pass null value for any required query params 2. Pass empty string value for required query params 3. Miss one of the required query params but pass valid values for other required params

Please help urgently as I am a beginner QA for testing end to end webservices.