You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: dns.go
    path of file: ./repos/k6/lib/types
    
    the code of the file until where you have to start completion: package types

import (
	"bytes"
	"encoding/json"
	"fmt"
	"strings"

	"gopkg.in/guregu/null.v3"
)

// DNSConfig is the DNS resolver configuration.
type DNSConfig struct {
	// If positive, defines how long DNS lookups should be returned from the
    
func (c *DNSConfig) unmarshal(params map[string]string) error {
	for k, v := range params {
		switch k {
		case "policy":
			p, err := DNSPolicyString(v)
			if err != nil {
				return err
			}
			c.Policy.DNSPolicy = p
			c.Policy.Valid = true
		case "select":
			s, err := DNSSelectString(v)
			if err != nil {
				return err
			}
			c.Select.DNSSelect = s
			c.Select.Valid = true
		case "ttl":
			c.TTL = null.StringFrom(v)
		default:
			return fmt.Errorf("unknown DNS configuration field: %s", k)
		}
	}
	return nil
}