Possible fix for U4-1466 which surfaced with the Standard MVC Starterkit package.

src/umbraco.cms/businesslogic/Content.cs

@@ -157,7 +157,7 @@ namespace umbraco.cms.businesslogic
             {
                 if (_contentTypeIcon == null && this.ContentType != null)
                     _contentTypeIcon = this.ContentType.IconUrl;
-                return _contentTypeIcon;
+                return _contentTypeIcon ?? string.Empty;
             }
             set
             {

src/umbraco.cms/businesslogic/web/Document.cs

@@ -1353,6 +1353,12 @@ namespace umbraco.cms.businesslogic.web
         [Obsolete("Obsolete", false)]
         protected override void setupNode()
         {
+            if (Id == -1 || Id == -20)
+            {
+                base.setupNode();
+                return;
+            }
+
             var content = Version == Guid.Empty
                            ? ApplicationContext.Current.Services.ContentService.GetById(Id)
                            : ApplicationContext.Current.Services.ContentService.GetByVersion(Version);