docs: private RolePlayerFragmentSet substituteRoleLabel(Stream<Role> roles) {
          Preconditions.checkNotNull(this.role());
          Preconditions.checkState(roleLabels() == null);
  
          ImmutableSet<Label> newRoleLabels =
                  roles.flatMap(Role::subs).map(SchemaConcept::label).collect(toImmutableSet());
  
          return new AutoValue_RolePlayerFragmentSet(
                  varProperty(), relation(), edge(), rolePlayer(), null, newRoleLabels, relationTypeLabels()
          );
      }