Name  string `xml:"Name"`
	Value string `xml:"Value"`
}

func (filter FilterRule) isEmpty() bool {
	return filter.Name == "" && filter.Value == ""
}

// MarshalXML implements a custom marshaller to support `omitempty` feature.
func (filter FilterRule) MarshalXML(e *xml.Encoder, start xml.StartElement) error {
	if filter.isEmpty() {
		return nil
	}
	type filterRuleWrapper FilterRule

	if !found {
		// Check for sub-prefix only if the input value is only a
		// single value, this rejects invalid inputs if any.
		found = !SubSystems.FuncMatch(strings.HasPrefix, subSystemValue[0]).IsEmpty() && len(subSystemValue) == 1
	}
	if !found {
		return nil, Errorf("unknown sub-system %s", s)
	}

	targets := Targets{}
	subSysPrefix := subSystemValue[0]
	if len(subSystemValue) == 2 {