docs: void registerCall(@NotNull ApolloCall call) {
      checkNotNull(call, "call == null");
      Operation operation = call.operation();
      if (operation instanceof Query) {
        registerQueryCall((ApolloQueryCall) call);
      } else if (operation instanceof Mutation) {
        registerMutationCall((ApolloMutationCall) call);
      } else {
        throw new IllegalArgumentException("Unknown call type");
      }
    }