code: @SuppressWarnings("MethodMayBeStatic")
    public void validate(Tag tag) {
      String relationIri = tag.getRelationIri();
      Relation relation = Relation.forIRI(relationIri);
      if (relation == null) {
        throw new MolgenisValidationException(
            new ConstraintViolation(format("Unknown relation IRI [%s]", relationIri)));
      }
    }
docs: Validates tag
  
  @param tag tag
  @throws MolgenisValidationException if tag is not valid