error: GraphQL interface trait method can't have default implementation
 --> fail/interface/trait/method_default_impl.rs:5:26
  |
5 |       fn id(&self) -> &str {
  |  __________________________^
6 | |         "default"
7 | |     }
  | |_____^
  |
  = note: https://spec.graphql.org/June2018/#sec-Interfaces