No Error render for custom mime type

[AmaliaMV]

I am using json view with Custom Mime Types. I have minimal and export mime types.

Additionally, a controller has an action which validates an object.

    def validate(Pet pet) {
        pet.validate()
        respond pet
    }

If I send an object with invalid data to "$baseUrl/pet/validate", the response will be 422 (the expected response). But if I send the same object to "$baseUrl/pet/validate?format=minimal", the response will be 404.

I created this tests to reproduce the issue:

    void "test validate a property without format"() {
        when:
        def resp = restBuilder().post("$baseUrl/pet/validate") {
            json ([name: 'invalid name'])
        }

        then:
        resp.status == 422
        resp.json.errors[0].field == "name"

    }

    void "test validate a property with specific format"() {
        when:
        def resp = restBuilder().post("$baseUrl/pet/validate?format=minimal") {
            json ([name: 'invalid name'])
        }

        then:
        resp.status == 422  // <-- this fail, the value is 404
        resp.json.errors[0].field == "name"
    }

Apparently, doesn't exist any error render registered to minimal mime type. So, https://github.com/grails/grails-core/blob/a16b4a4274025cc337b3b7dc4463bcad464f2ab9/grails-plugin-rest/src/main/groovy/grails/artefact/controller/RestResponder.groovy#L170 is executed. The same happens with export format.

Here the link to the sample app: https://github.com/AmaliaMV/gsonView-errorWithFormat