Sendgrid-nodejs: Uncaught Syntax Error: Unexpected token < (in lib/sendgrid.js triggered on a response object)

Issue Summary

After sending out a templated email using SendGrid's email helper utility. The server response from SendGrid's API is returning invalid JSON according to this wrapper (sendgrid-nodejs).

Uncaught SyntaxError: Unexpected token <
      at Object.parse (native)
      at node_modules/sendgrid/lib/sendgrid.js:110:42
      at IncomingMessage.<anonymous> (node_modules/sendgrid/node_modules/sendgrid-rest/lib/client.js:108:9)
      at endReadableNT (_stream_readable.js:921:12)

Line 110 is:

  //Use callback
  self.client.API(request, function(response) {
    response.body = response.body ? JSON.parse(response.body) : response.body;

Steps to Reproduce

1. Ensure sendgrid node package -->"sendgrid": "^4.7.1",
2. Create a template with substitutions in SendGrid and activate that template
3. Create a full email for the template using the email helper. apply .toJSON at end.

Example:

const BaseWelcomeEmail = (function(){
    const helper = require('sendgrid').mail,
        from_email = new helper.Email(testEmail),
        to_email = new helper.Email(testEmail),
        subject = "Welcome to Bedly",
        content = new helper.Content("text/plain", "hello"),

        mail = new helper.Mail(from_email, subject, to_email, content),
        personalization = new helper.Personalization();

    let substitution = new helper.Substitution(":firstname", "Aaron");

    personalization.addSubstitution(substitution);
    substitution = new helper.Substitution(":lastname", "Elk");
    personalization.addSubstitution(substitution);
    substitution = new helper.Substitution(":address", "96 Washington Avenue");
    personalization.addSubstitution(substitution);
    substitution = new helper.Substitution(":neighborhood", "Washington Heights");
    personalization.addSubstitution(substitution);
    substitution = new helper.Substitution(":unitNumber", "N/A");
    personalization.addSubstitution(substitution);
    substitution = new helper.Substitution(":roomNumber", "2J");
    personalization.addSubstitution(substitution);

    mail.addPersonalization(personalization);

    return mail;
})();

You can even create a mocha test, I ran this from this test environment:

    describe('Test Email Template', function () {
        it('test template ${TEMPLATE_ID} is active and is complete', function (done) {
            BaseWelcomeEmail.setTemplateId(TEMPLATE_ID);
            SendEmailImpl.sendEmail(BaseWelcomeEmail.toJSON(), done, function(error, response){
                assert_OKResponse(error, response, done);
            });
        });
    });

The sendEmail function contains the normal POST V3 setup to call the APIas described in the documents.

Technical details:

• sendgrid-nodejs Version: 4.7.1
• Node.js Version: 4.6.1