code: public static String getHub() throws InvalidHubException {
          String hub = getProgramProperty(HUB);
          if (hub == null || "".equals(hub)) {
              throw new InvalidHubException("Hub isn't set");
          }
          return hub;
      }
docs: Retrieves the hub property if it is set. This could be to sauce, grid, or any other cloud tool.
  This should be provided with the protocol and address, but leaving out the /wd/hub
  
  @return String: the set hub address, null if none are set