code: func GetNII(o dhcp6.Options) (*NII, error) {
  	v, err := o.GetOne(dhcp6.OptionNII)
  	if err != nil {
  		return nil, err
  	}
  
  	n := new(NII)
  	err = n.UnmarshalBinary(v)
  	return n, err
  }
docs: // GetNII returns the Client Network Interface Identifier Option value,
  // described in RFC 5970, Section 3.4.
  //
  // The NII value returned indicates a client's level of Universal Network
  // Device Interface (UNDI) support.