Missing element shouldn't be fatal

[pushred]

If SubscribeEmail is instantiated on a page without the specified element it currently blows up like this:

Uncaught TypeError: Cannot read property 'id' of null
scripts.js:2283 _setDefaults
scripts.js:2200 SubscribeEmail
scripts.js:393 module.exports
scripts.js:486 (anonymous function)
scripts.js:25725 jQuery.Callbacks.fire
scripts.js:25837 jQuery.Callbacks.self.fireWith
scripts.js:26043 jQuery.extend.ready
scripts.js:26059 completed

//get/set the ID of the HTML element (may be different than the value of element)
options.id = instance.theForm.id || ('subscribe-email-' + options.service);

This error isn't horrible, but it could handle things a bit better for what's probably going to be a fairly common scenario. I think it should throw and log a more direct, helpful error.