Fixes an issue with subsequent value updates not being tracked if the…

[dxmo]

… value was set to null

fixes #643

[snewcomer]

@dxmo Looks like some test failures

[dxmo]

@snewcomer I've had a further look and while my PR somewhat address the issue for me, its not a valid fix - please ignore it and apologies.

However, I was able to track this down to ember-changeset, specifically the value is actually not being set on the object at all - I have no idea why would that be at the moment. Still trying to understand it ... but essentially the code bellow does not result in the object being updated with the passed value. I understand safeGet is actually Ember.set() which makes it all the more suspicious ..

line 63 : ember-changeset/addon/index.js:

  safeSet(obj, key, value) {
    return safeSet(obj, key, value);
  }

[snewcomer]

@dxmo Thanks for the update! If there was a failing test your could write and push to a PR, that would help greatly in finding a solution for you!