assertEquals(Schema.Type.STRING, response.getTypes().get(1).getType());
// check request schema is union
Schema request = message.getRequest();
Field field = request.getField("s");
assertNotNull("field 's' should not be null", field);
Schema param = field.schema();
assertEquals(Schema.Type.UNION, param.getType());
assertEquals(Schema.Type.NULL, param.getTypes().get(0).getType());
assertEquals(Schema.Type.STRING, param.getTypes().get(1).getType());
// check union erasure
assertEquals(String.class, ReflectData.get().getClass(response));