type FilterRule struct {
	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

// 2. the value of the parameter in the config store if set,
// 3. the default value,
//
// This function only works for a subset of sub-systems, others return
// `ValueSourceAbsent`. FIXME: some parameters have custom environment
// variables for which support needs to be added.
//
// When redactSecrets is true, the returned value is empty if the configuration
// parameter is a secret, and the returned isRedacted flag is set.