code: public boolean isSet(_Fields field) {
      if (field == null) {
        throw new IllegalArgumentException();
      }
  
      switch (field) {
      case NUM_CPUS:
        return isSetNumCpus();
      case NETWORK_MBPS:
        return isSetNetworkMBps();
      case MEMORY_MB:
        return isSetMemoryMB();
      case DISK_GB:
        return isSetDiskGB();
      }
      throw new IllegalStateException();
    }
docs: Returns true if field corresponding to fieldID is set (has been assigned a value) and false otherwise