public void next(Knoop knoop) {
    @SuppressWarnings("unchecked")
    Enum<? extends Diagnose> diagnose = (Enum<? extends Diagnose>) knoop.getDiagnose();
    Enum<? extends Diagnose>[] diagnoses = possibleDiagnoses().getEnumConstants();

    knoop.setDiagnose((Diagnose) diagnoses[(diagnose.ordinal() + 1) % diagnoses.length]);
  }