prow/config/branch_protection.go
func unionStrings(parent, child []string) []string {
	if child == nil {
		return parent
	}
	if parent == nil {
		return child
	}
	s := sets.NewString(parent...)
	s.Insert(child...)
	return s.List()
}
func unionStrings(parent, child []string) []string {
	if child == nil {
		return parent
	}
	if parent == nil {
		return child
	}
	s := sets.NewString(parent...)
	s.Insert(child...)
	return s.List()
}
// unionStrings merges the parent and child items together