When data is undefined, registry should 500

[matteofigus]

This happens when a component calls a callback without an error, but also without the data object.
At the moment, in some scenarios, the registry just times-out.

When a view doesn't require a view-model, either an empty object should be called-back as result, or a component should have an empty data field in its package.json (to declare it doesn't require any logic to work).

Example:

module.exports.data = function(cx, cb){
  var data;
  cb(null);
};

[matteofigus]

Can you review this today @mattiaerre or @pbazydlo?

[mattiaerre]

Hi @matteofigus I am looking at this now ... bear w/ me 😉

[pbazydlo]

i'm leaving it to you then @mattiaerre

[mattiaerre]

LGTM

// cc @matteofigus @pbazydlo