code: func mergeDNSOptions(existingDNSConfigOptions []string, dnsConfigOptions []v1.PodDNSConfigOption) []string {
  	optionsMap := make(map[string]string)
  	for _, op := range existingDNSConfigOptions {
  		if index := strings.Index(op, ":"); index != -1 {
  			optionsMap[op[:index]] = op[index+1:]
  		} else {
  			optionsMap[op] = ""
  		}
  	}
  	for _, op := range dnsConfigOptions {
  		if op.Value != nil {
  			optionsMap[op.Name] = *op.Value
  		} else {
  			optionsMap[op.Name] = ""
  		}
  	}
  	// Reconvert DNS options into a string array.
  	options := []string{}
  	for opName, opValue := range optionsMap {
  		op := opName
  		if opValue != "" {
  			op = op + ":" + opValue
  		}
  		options = append(options, op)
  	}
  	return options
  }
docs: // mergeDNSOptions merges DNS options. If duplicated, entries given by PodDNSConfigOption will
  // overwrite the existing ones.