code: public String getClient()
      {
          String client = null;
          if (this.properties != null)
          {
              client = (String) this.properties.get(PersistenceProperties.KUNDERA_CLIENT_FACTORY);
          }
  
          if (client == null)
          {
              log.error("kundera.client property is missing for persistence unit:" + persistenceUnitName);
              throw new IllegalArgumentException("kundera.client property is missing for persistence unit:"
                      + persistenceUnitName);
          }
  
          return client;
      }
docs: Gets the client. In case client is not configure, it throws
  IllegalArgumentException.
  
  @return the client