code: public void returnReservedValues(Log log) {
          for (SequenceValueProducer producer : values()) {
              try {
                  producer.returnReservedValues();
              } catch (RepositoryException e) {
                  if (log == null) {
                      log = LogFactory.getLog(SequenceValueProducerPool.class);
                  }
                  log.error(e.getMessage(), e);
              }
          }
      }
docs: Returns reserved values for all {@link SequenceValueProducer}s.
  
  @param log optional log to report errors; uses default log if null