Hi Tobias,

What do you mean backend? Are you using webApiUmbraco controller or surfaceController?

Maybe Umbraco helper is null?

Thanks

The grid editors preview in the umbraco. Nope i'm not using one of these. Already thought of that.

I'm getting this intermittently on the front-end (v.7.4.3). Publishing the entire site appears to get rid of it.

[NullReferenceException: Object reference not set to an instance of an object.]

   umbraco.presentation.preview.PreviewContent.EnsureInitialized(User user, String previewSet, Boolean validate, Action initialize) +88
   Umbraco.Web.PublishedCache.XmlPublishedCache.PublishedContentCache.<get_GetXmlDelegate>b__3(UmbracoContext context, Boolean preview) +132
   Umbraco.Web.PublishedCache.XmlPublishedCache.PublishedContentCache.GetXml(UmbracoContext umbracoContext, Boolean preview) +28
   Umbraco.Web.PublishedCache.XmlPublishedCache.PublishedContentCache.GetById(UmbracoContext umbracoContext, Boolean preview, Int32 nodeId) +20
   Umbraco.Web.PublishedCache.XmlPublishedCache.PublishedContentCache.DetermineRouteById(UmbracoContext umbracoContext, Boolean preview, Int32 contentId) +35
   Umbraco.Web.PublishedCache.XmlPublishedCache.PublishedContentCache.GetRouteById(UmbracoContext umbracoContext, Boolean preview, Int32 contentId) +86
   Umbraco.Web.Routing.DefaultUrlProvider.GetUrl(UmbracoContext umbracoContext, Int32 id, Uri current, UrlProviderMode mode) +96
   Umbraco.Web.Routing.<>c__DisplayClass3.<GetUrl>b__0(IUrlProvider provider) +28
   System.Linq.WhereSelectArrayIterator`2.MoveNext() +66
   System.Linq.Enumerable.FirstOrDefault(IEnumerable`1 source, Func`2 predicate) +94
   Umbraco.Web.Routing.UrlProvider.GetUrl(Int32 id, Uri current, UrlProviderMode mode) +169
   Umbraco.Web.Templates.TemplateUtilities.ParseInternalLinks(String text) +285
   Umbraco.Web.Templates.TemplateUtilities.ParseInternalLinks(String text, Boolean preview) +80
   Umbraco.Web.PropertyEditors.ValueConverters.RteMacroRenderingValueConverter.ConvertDataToSource(PublishedPropertyType propertyType, Object source, Boolean preview) +71
   Umbraco.Web.PublishedCache.XmlPublishedCache.XmlPublishedProperty.<.ctor>b__0() +39
   System.Lazy`1.CreateValue() +415
   System.Lazy`1.LazyInitValue() +152
   System.Lazy`1.get_Value() +75
   Umbraco.Web.PublishedCache.XmlPublishedCache.XmlPublishedProperty.<.ctor>b__1() +20
   System.Lazy`1.CreateValue() +415
   System.Lazy`1.LazyInitValue() +152
   System.Lazy`1.get_Value() +75
   Umbraco.Web.PublishedCache.XmlPublishedCache.XmlPublishedProperty.get_Value() +9
   Umbraco.Web.PublishedPropertyExtension.GetValue(IPublishedProperty property, Boolean withDefaultValue, T defaultValue) +73
   Umbraco.Web.PublishedContentExtensions.GetPropertyValue(IPublishedContent content, String alias, Boolean recurse, Boolean withDefaultValue, T defaultValue) +82
   Umbraco.Web.PublishedContentExtensions.GetPropertyValue(IPublishedContent content, String alias) +59

The null reference exception is coming from umbraco.presentation.preview.PreviewContent.EnsureInitialized - so it's a case of figuring out what is null and why.

The latest source code for that method is...

public void EnsureInitialized(User user, string previewSet, bool validate, Action initialize)
{
    lock (_initLock)
    {
        if (_initialized) return;

        _userId = user.Id;
        ValidPreviewSet = UpdatePreviewPaths(new Guid(previewSet), validate);
        initialize();
        _initialized = true;
    }
}

For ref: https://github.com/umbraco/Umbraco-CMS/blob/dev-v7/src/Umbraco.Web/umbraco.presentation/umbraco/preview/PreviewContent.cs#L48

Breaking it down, the null reference is either coming from the user object or previewSet value.

The user object shouldn't be null, since you are already logged into the back-office, (unless there's something else corrupted and that'd be worrying).

If you want to check this, in your view/partial add this: @(UmbracoContext.Current.Security.CurrentUser) - if that throws a null reference, that's the issue

The previewSet value might be wrong or invalid. Check your browser to see if you have a cookie called "UMB_PREVIEW" and that the value looks like a GUID. If it's not there or doesn't look like a GUID, then that's the issue - clear your cookies and try again.

I hope this helps?

Cheers, - Lee

It "worked" :P

What I did:

1. Open the node with the grid editor - got the error from above
2. Checked the cookies - no umb_preview cookie
3. Opened the actual preview mode - umb_preview cookie present
4. Went back to the grid editor - now it renders the previews correctly without error and the umb_preview cookie is also present.

So it doesn't create the preview correctly, am i right?

Hi Lee,

I don't think it's DTGE - I'm seeing this error (on Umbraco 7.4.3), and it seems to be related to a standard Rich Text field (specifically, to Umbraco.Web.Templates.TemplateUtilities.ParseInternalLinks). This is hitting the XmlPublishedCache and then dropping into umbraco.presentation.preview.PreviewContent.EnsureInitialized - it's doing it regardless of whether the request contains any Umbraco back office cookies (I get the same when accessing the site with a browser which is logged into the back office and one that isn't - in fact, I picked the issue up when running a spider across the site).

This is the stack trace I have:

2016-10-10 12:06:39,821 [P13028/D4/T79] ERROR Umbraco.Core.UmbracoApplicationBase - An unhandled exception occurred

System.NullReferenceException: Object reference not set to an instance of an object.

at umbraco.presentation.preview.PreviewContent.EnsureInitialized(User user, String previewSet, Boolean validate, Action initialize)

at Umbraco.Web.PublishedCache.XmlPublishedCache.PublishedContentCache.<get_GetXmlDelegate>b__3(UmbracoContext context, Boolean preview)

at Umbraco.Web.PublishedCache.XmlPublishedCache.PublishedContentCache.GetXml(UmbracoContext umbracoContext, Boolean preview)

at Umbraco.Web.PublishedCache.XmlPublishedCache.PublishedContentCache.GetById(UmbracoContext umbracoContext, Boolean preview, Int32 nodeId)

at Umbraco.Web.PublishedCache.ContextualPublishedCache`1.GetById(Boolean preview, Int32 contentId)

at Umbraco.Extensions.UrlProvider.CustomCachedUrlProvider.GetUrl(UmbracoContext umbracoContext, Int32 id, Uri current, UrlProviderMode mode)

at Umbraco.Web.Routing.UrlProvider.<>c__DisplayClass3.<GetUrl>b__0(IUrlProvider provider)

at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()

at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source, Func`2 predicate)

at Umbraco.Web.Routing.UrlProvider.GetUrl(Int32 id, Uri current, UrlProviderMode mode)

at Umbraco.Web.Templates.TemplateUtilities.ParseInternalLinks(String text)

at Umbraco.Web.Templates.TemplateUtilities.ParseInternalLinks(String text, Boolean preview)

at Umbraco.Web.PropertyEditors.ValueConverters.RteMacroRenderingValueConverter.ConvertDataToSource(PublishedPropertyType propertyType, Object source, Boolean preview)

at Umbraco.Web.PublishedCache.XmlPublishedCache.XmlPublishedProperty.<.ctor>b__0()

at System.Lazy`1.CreateValue()

at System.Lazy`1.LazyInitValue()

at System.Lazy`1.get_Value()

at Umbraco.Web.PublishedCache.XmlPublishedCache.XmlPublishedProperty.<.ctor>b__1()

at System.Lazy`1.CreateValue()

at System.Lazy`1.LazyInitValue()

at System.Lazy`1.get_Value()

at Umbraco.Web.PublishedCache.XmlPublishedCache.XmlPublishedProperty.get_Value()

at Umbraco.Web.PublishedPropertyExtension.GetValue[T](IPublishedProperty property, Boolean withDefaultValue, T defaultValue)

at Umbraco.Web.PublishedContentExtensions.GetPropertyValue[T](IPublishedContent content, String alias, Boolean recurse, Boolean withDefaultValue, T defaultValue)

at Umbraco.Web.PublishedContentExtensions.GetPropertyValue[T](IPublishedContent content, String alias)

at Umbraco.Web.PublishedContentModels.FaqQuestion.get_Answer()

at Umbraco.Extensions.Controllers.HelpAdviceController.<>c.<SearchFaqsList>b__1_0(FaqQuestion faq)

Republishing the site doesn't seem to help.

Note that the FaqQuestion content type does not have a grid editor on it.

Okay, this issue has reared it's ugly head again for us - but I think I've got somewhere with it (at least in our specific setup).

The key was these lines from the stack trace:

at Umbraco.Web.PublishedCache.ContextualPublishedCache`1.GetById(Boolean preview, Int32 contentId)
at Umbraco.Extensions.UrlProvider.CustomCachedUrlProvider.GetUrl(UmbracoContext umbracoContext, Int32 id, Uri current, UrlProviderMode mode)

On this site we use a custom URL provider, which made a call to GetById on the content cache:

content = umbracoContext.ContentCache.GetById(id);

Note that it was using the method which takes only a content ID and not the boolean preview switch - however, the stack trace shows execution passing directly to the version of the method with takes both parameters - so presumably the compiler has optimised this step away?

Digging in the Umbraco source code I found that the ID only method is defined on Umbraco.Web.PublishedCache.ContextualPublishedCache (which the actual instance UmbracoContext.ContentCache inherits from via several levels - it's in fact a ContextualPublishedContentCache). This method sets the preview mode from the UmbracoContext:

public IPublishedContent GetById(int contentId)
{
    return GetById(UmbracoContext.InPreviewMode, contentId);
}

But what will preview be set to if the compiler has bypassed this method? Good question! Clearly it can sometimes be true even when it definitely shouldn't be.

So, the fix in our case has been to explicitly set preview to false:

content = umbracoContext.ContentCache.GetById(false, id);

I'm still testing this, so I'm not sure if it'll have any nasty side effects. Arguably I should be passing UmbracoContext.InPreviewMode rather than false, so I may have issues when it really is previewing.

It's also worth noting that the intermittent nature of the issue on this site may simply have been down to caching - the custom URL provider checks for cached results before it reaches the GetById call, so if the URL for the content ID has already been successfully looked up that'll be returned without a problem.

There is still the rather obvious unsolved question; why do we only have this issue when the URL provider is called in the context of resolving URLs in RTE content? I've added debug output and confirmed this is definitely the case (when we hit this issue we're always resolving the URL of a content ID in RTE markup - yet the same ID is resolved without a problem elsewhere). But I've no idea why the code would behave differently - unless the stack trace is not actually correct and the ID only GetById method is called, and for some reason when parsing the RTE content UmbracoContext.InPreviewMode is true...which would be truly horrible...

Worth adding to this that after further testing, setting the preview parameter to UmbracoContext.InPreviewMode doesn't fix the problem - only hard coding it to false.

So, it appears that somewhere within the RTE content parsing the preview mode is switched on - though quite why mystifies me.

I would appear that the stack trace bypassing the ID only method was a red herring.

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