[Bug canary] @tracked with uninitialized property throws runtime error

[chriskrycho]

If you write a component like this:

import Component from '@glimmer/component';
import { tracked } from '@glimmer/tracking';

export default class ItBroken extends Component {
  @tracked data;

  get ugh() {
    return this.data;
  }
}

{{this.ugh}}

Then you see this error:

null is not an object (evaluating 'initializer.call')

The problem is here – it should check for both null and undefined.