title: Umbraco website throws NullReferenceException on existing objects
body: <p>I'm using UmbracoCms 7.12 for my website with <code>LiveAppData</code> Models Builder.</p>
  
  <p>At the backend I've created required DocumentTypes(aka Models) and Views/Partial Views for them.</p>
  
  <p>Following code of Partial View throws NullReferenceException on execute.
  When I'm going Debug mode, the objects realy exist and calling testimonialItems[0] returns not-null object. Proofs are in screenshots below.
  TestimonialsSection - is Document Type with Children of TestimonialItem.
  At the backend I've created 2 children inside him.</p>
  
  <p>The following code throws at <code>var testi = testimonialItems[i];</code> line. Even if I comment this line, it starts throwing <code>@header</code> NullReferenceException.</p>
  
  <pre><code>@inherits UmbracoTemplatePage&lt;TestimonialsSection&gt;
  @{
  
  
      var testimonialItems = this.Model.Content.Children&lt;TestimonialItem&gt;().ToList();
  
      var header = this.Model.Content.Header;
  
      var body = this.Model.Content.Body;
  }
  
  
  @{
      &lt;div id="testimonials" class="testimonials-section"&gt;
          &lt;div class="container"&gt;
              &lt;h2 class="section-title text-center"&gt;@header&lt;/h2&gt;
  
              @for (var i = 0; i &lt; testimonialItems.Count; i++)
              {
                  var testi = testimonialItems[i];
  
                  &lt;div class="item mx-auto @(i % 2 == 0 ? "" : "item-reversed")"&gt;
                      &lt;div class="profile-holder"&gt;
                          &lt;img class="profile-image" src="@testi.Image.Url" alt="profile"&gt;
                      &lt;/div&gt;
                      &lt;div class="quote-holder"&gt;
                          &lt;blockquote class="quote"&gt;
                              &lt;p&gt;@testi.Body&lt;/p&gt;
                              &lt;div class="quote-source"&gt;
                                  &lt;span class="name"&gt;@testi.Header&lt;/span&gt;
                              &lt;/div&gt;
                          &lt;/blockquote&gt;
                      &lt;/div&gt;
                  &lt;/div&gt;
              }
  
          &lt;/div&gt;
      &lt;/div&gt;
  }
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/po7CN.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/po7CN.png" alt="enter image description here"></a>
  <a href="https://i.stack.imgur.com/0wcJJ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/0wcJJ.png" alt="enter image description here"></a></p>