title: First item in errors() is [null]
body: <p>I have the following code:    </p>
  
  <pre><code>function JobTask() {
      var self = this;
  
      self.description = ko.observable('').extend({
          required: true
      });
      self.priority = ko.observable('').extend({
          number: true,
          required: true
      });
      self.complete = ko.observable(false);
  }
  
  function CreateJobViewModel() {
      var self = this;
  
      self.task = ko.observable(new JobTask());
  
      self.taskErrors = ko.validation.group(self.task);
      self.addTask = function () {
  
          if (self.taskErrors().length) {
              console.log(self.taskErrors());
              self.taskErrors.showAllMessages();
          }
          else {
              ...
          }
      };
  }
  </code></pre>
  
  <p>The problem is, when I add a task, it is invalid for some reason even when I have entered in the fields correctly. The console outputs <code>[null]</code>. Upon further investigation, it seems that even when I don't enter my fields correctly, the first item in my <code>taskErrors</code> array is always <code>[null]</code>. So it may looks like: <code>[null], "This field is required."</code>. Not sure what I've done wrong?</p>
  
  <h2>Edit</h2>
  
  <p>Here is a fiddle I created of the problem: <a href="http://jsfiddle.net/5kh6h/1/" rel="nofollow">http://jsfiddle.net/5kh6h/1/</a></p>