docs: private PersistenceBroker obtainBroker()
      {
          PersistenceBroker _broker;
          try
          {
              if (pbKey == null)
              {
                  //throw new OJBRuntimeException("Not possible to do action, cause no tx runnning and no PBKey is set");
                  log.warn("No tx runnning and PBKey is null, try to use the default PB");
                  _broker = PersistenceBrokerFactory.defaultPersistenceBroker();
              }
              else
              {
                  _broker = PersistenceBrokerFactory.createPersistenceBroker(pbKey);
              }
          }
          catch (PBFactoryException e)
          {
              log.error("Could not obtain PB for PBKey " + pbKey, e);
              throw new OJBRuntimeException("Unexpected micro-kernel exception", e);
          }
          return _broker;
      }