code: static Set<String> validatePlaysAndRelatesStructure(Casting casting) {
          Set<String> errors = new HashSet<>();
  
          //Gets here to make sure we traverse/read only once
          Thing thing = casting.getRolePlayer();
          Role role = casting.getRole();
          Relation relation = casting.getRelation();
  
          //Actual checks
          roleNotAllowedToBePlayed(role, thing).ifPresent(errors::add);
          roleNotLinkedToRelation(role, relation.type(), relation).ifPresent(errors::add);
  
          return errors;
      }
docs: This method checks if the plays edge has been added between the roleplayer's Type and
  the Role being played.
  It also checks if the Role of the Casting has been linked to the RelationType of the
  Relation which the Casting connects to.
  
  @return Specific errors if any are found