Meteor 1.3 passing variable data to Npm module

1

I found a strange issue using the Npm dns module in Meteor 1.3.

This works:

var dns = Npm.require('dns');

dns.resolve4(server_name, (err, addresses) => {
	if (err) throw err;

});
2

Sorry this works:

var dns = Npm.require('dns');

dns.resolve4('mycloud.com', (err, addresses) => {
});

This does NOT:

const server_name = process.env.METEOR_SERVER_NAME.toString();

var dns = Npm.require('dns');

dns.resolve4(server_name, (err, addresses) => {
	if (err) throw err;
});

The error gets thrown.
Any suggestions as to what the issue is???