prow/flagutil/strings.go
func (s *Strings) Set(value string) error {
	if !s.beenSet {
		s.beenSet = true
		// Value is being set, don't use default.
		s.vals = nil
	}
	s.vals = append(s.vals, value)
	return nil
}
func (s *Strings) Set(value string) error {
	if !s.beenSet {
		s.beenSet = true
		// Value is being set, don't use default.
		s.vals = nil
	}
	s.vals = append(s.vals, value)
	return nil
}
// Set records the value passed