code: public OperationFuture<List<Server>> addPublicIp(ServerFilter serverFilter,  CreatePublicIpConfig publicIpConfig) {
          return addPublicIp(Arrays.asList(getRefsFromFilter(serverFilter)), publicIpConfig);
      }
docs: Add public IP to list servers
  
  @param serverFilter   server search criteria
  @param publicIpConfig publicIp config
  @return OperationFuture wrapper for list of ServerRef