@@ -27,5 +27,8 @@ func (o *IpOpt) Set(val string) error {

 }

 func (o *IpOpt) String() string {

+	if *o.IP == nil {

+		return ""

+	}

 	return o.IP.String()

 }

@@ -2,6 +2,7 @@ package opts

 import (

 	"fmt"

+	"net"

 	"strings"

 	"testing"

 )

@@ -179,6 +180,18 @@ func TestValidateExtraHosts(t *testing.T) {

 	}

 }

+func TestIpOptString(t *testing.T) {

+	addresses := []string{"", "0.0.0.0"}

+	var ip net.IP

+

+	for _, address := range addresses {

+		stringAddress := NewIpOpt(&ip, address).String()

+		if stringAddress != address {

+			t.Fatalf("IpOpt string should be `%s`, not `%s`", address, stringAddress)

+		}

+	}

+}

+

 func logOptsValidator(val string) (string, error) {

 	allowedKeys := map[string]string{"max-size": "1", "max-file": "2"}

 	vals := strings.Split(val, "=")