I need a bit more detail. Are you using one of the RAML 2... projects.. and trying to find a way for the auto generated code to validate incoming request query params? RAML simply defines the API. How you use RAML to generate code or other artifacts is outside of the RAML definition/tools itself. In other words, if you are using RAML2JAXRS to generate code from RAML (and presumably JSON Schema), you have to implement the logic to determine if a query parameter is invalid or not. However, in the case of RAML2JAXRS, it builds method signatures that only pass in the query parameters defined in RAML.
Not entirely sure if I am understanding the question though.