title: this.get('x') returns ' undefined' instead of 'undefined'
body: <p>In a form-component I have an observer that tests if a property is valid before to start further validations.<br>
  So I checked if the property has not yet been defined (happens at initialization f.e.)</p>
  
  <pre><code>if(typeof this.get('myProperty') !== 'undefined') { 
      //do smth 
  }
  </code></pre>
  
  <p>Then I realized that <code>this.get</code> would not return a type of 'undefined' but a string with the value undefined.<br>
  Fair enough.</p>
  
  <p><strong>BUT</strong></p>
  
  <pre><code>console.log(this.get('myProperty'));
  </code></pre>
  
  <p>gives me ' undefined' instead of 'undefined' - notice the space before 'undefined'!</p>
  
  <p>Is this a bug?<br>
  Or do I really have to check for ' undefined' with a space and is there a reason for that?</p>
  
  <p><em>Ember-cli: 1.13.7<br>
  Ember: 2.0.1</em></p>