Optional parameters Typescript

So I have this:

/**
     * sendNewsletterEmail
     * @param { SibApiV3Sdk.SendSmtpEmailTo[] } to 
     * @param { NewsEmailTemplate } template 
     * @param { TObject } params 
     * @param { SibApiV3Sdk.SendSmtpEmailAttachment[] } attachment 
     * @param { IUsersParsed } bccUsers 
     * @return { Promise<ISibApiV3CreateResponse> }
     */
    public static async sendNewsletterEmail(
        to: SibApiV3Sdk.SendSmtpEmailTo[],
        template: NewsEmailTemplate,
        params: TObject,
        attachment?: SibApiV3Sdk.SendSmtpEmailAttachment[],
        bccUsers?: IUsersParsed[]
    ): Promise<ISibApiV3CreateResponse> {
...}

Problem is whenever I don't pass the attachment parameter and pass the bcc one I get an error because bcc is read as the attachment param. What can I do to solve it?

Im calling it like this (I know its missing the if/else for bcc too)

if (emailAttachments.length) {
            response = await EmailMembership.sendNewsletterEmail(sendTo, template, params, emailAttachments, parsedBcc);
        } else {
            response = await EmailMembership.sendNewsletterEmail(sendTo, template, params, parsedBcc);
        }