email-templates: Error: Cannot find module 'underscore'

Seems that upon installing email-templates and pug, by importing email-templates I get the following error:

The code I’m using is quite simple:

const Email = require("email-templates");

const email = new Email({
    message: { from: fromAddr },
    send: true,
    transport: __transport
});
email
    .send({
        template,
        message: { to: toAddr },
        locals: Object.assign({
            emailID
        }, properties)
    });

__transport is a Nodemailer transport instance:

__transport = nodemailer.createTransport({
    SES: getSES()
});

I’m running this on Node 10 in a docker container. Everything installs fine, but I get that error when I try to run that code. I’m using Nodemailer v4.6.8 and email-templates v5.0.0.