sending email with optional attachment in gomail v2

I have a package mystuff which deals with sending an email.

package mystuff

import (
    "crypto/tls"
    "gopkg.in/gomail.v2"
)

type Params struct {
    From, To, Subject, Body, Filename string
}

func Mail(p Params) (err error) {
    m := gomail.NewMessage()
    m.SetHeader("From", p.From)
    m.SetHeader("To", p.To)
    m.SetHeader("Subject", p.Subject)
    m.SetBody("text/plain", p.Body)
    m.Attach(p.Filename)

    d := gomail.Dialer{Host: "smtp.example.com", Port: 25}
    d.TLSConfig = &tls.Config{InsecureSkipVerify: true}
    if err := d.DialAndSend(m); err != nil {
        panic(err)
    }
    return
}

and the main paskage which sends the email

package main

import . "mystuff"

func main() {
    Mail(Params{From: "example@example.com", To: "some@gmail.com", Subject: "Sub", Body: "B", Filename: "/tmp/image.jpg" })
}

I would like to make Filename as an optional parameter.

for example

    Mail(Params{From: "example@example.com", To: "some@gmail.com", Subject: "Sub", Body: "B" })
}

Thank you

With filename as optional parameter, you have to check for the length on params filename (string is initialized empty):

func Mail(p Params) (err error) {
    m := gomail.NewMessage()
    m.SetHeader("From", p.From)
    m.SetHeader("To", p.To)
    m.SetHeader("Subject", p.Subject)
    m.SetBody("text/plain", p.Body)
    if len(p.Filename)>0 {
        m.Attach(p.Filename)
    }

    d := gomail.Dialer{Host: "smtp.example.com", Port: 25}
    d.TLSConfig = &tls.Config{InsecureSkipVerify: true}
    if err := d.DialAndSend(m); err != nil {
        panic(err)
    }
    return
}