title: @Umbraco.TypedMedia(MyProperty) is null in Umbraco 7.6.1
body: <p>I'm using Umbraco 7.6.1 and I'm trying to get the url for a media image using the code below in razor.</p>
  
  <pre><code>@{
     var bannerMediaItem = Umbraco.TypedMedia(Model.Content.Image); 
     var bannerUrl = bannerMediaItem.Url;
  }
  </code></pre>
  
  <p>But bannerMediaItem is always null even though I know it exists. If I do this..</p>
  
  <pre><code>@Model.Content.Image
  </code></pre>
  
  <p>It returns the id of the image e.g. 1086</p>