code: public Set<Integer> getAvailablePorts(SupervisorDetails supervisor) {
          Set<Integer> usedPorts = this.getUsedPorts(supervisor);
  
          Set<Integer> ret = new HashSet<>();
          ret.addAll(getAssignablePorts(supervisor));
          ret.removeAll(usedPorts);
  
          return ret;
      }
docs: Return the available ports of this supervisor.