code: func GetParameterRequestList(o dhcp4.Options) OptionCodes {
  	v := o.Get(dhcp4.OptionParameterRequestList)
  	if v == nil {
  		return nil
  	}
  	var oc OptionCodes
  	if err := (&oc).UnmarshalBinary(v); err != nil {
  		return nil
  	}
  	return oc
  }
docs: // GetParameterRequestList returns the list of requested DHCP option codes in
  // `o`.
  //
  // This returns nil if the option is not present or did not contain a valid
  // value.
  //
  // The parameter request list option is defined by RFC 2132, Section 9.8.