docs: private static DefaultDuration computeReevaluationInterval(final Integer inputReevaluationInterval,  int prevTimeSinceEarliestUnpaidInvoice, int curTimeSinceEarliestUnpaidInvoice) {
          if (inputReevaluationInterval != null && inputReevaluationInterval > 0) {
              return new DefaultDuration().setUnit(TimeUnit.DAYS).setNumber(inputReevaluationInterval);
          }
  
          if (prevTimeSinceEarliestUnpaidInvoice == -1) {
              return null;
          }
  
          Preconditions.checkState(prevTimeSinceEarliestUnpaidInvoice - curTimeSinceEarliestUnpaidInvoice > 0);
  
          return new DefaultDuration().setUnit(TimeUnit.DAYS).setNumber(prevTimeSinceEarliestUnpaidInvoice - curTimeSinceEarliestUnpaidInvoice);
      }