Html.ValidationSummary(ValidationSummary.All) throws NullReferenceException

[rsheptolut]

This started after I've updated my project from RC1 to ASP.NET Core 1.0. The tag helper also throws this exception.
If instead you specify ValidationSummary.ModelOnly, there's no exception. But also no property-level errors, which is bad.
Workarond: traverse ViewData.ModelState.Values manually and generate appropriate html markup.

Stack trace:

System.NullReferenceException.
   в Microsoft.AspNetCore.Mvc.ViewFeatures.Internal.ValidationHelpers.Visit(ModelStateDictionary dictionary, ModelStateEntry modelStateEntry, ModelMetadata metadata, List1 orderedModelStateEntries)
   в Microsoft.AspNetCore.Mvc.ViewFeatures.Internal.ValidationHelpers.Visit(ModelStateDictionary dictionary, ModelStateEntry modelStateEntry, ModelMetadata metadata, List1 orderedModelStateEntries)
   в Microsoft.AspNetCore.Mvc.ViewFeatures.Internal.ValidationHelpers.GetModelStateList(ViewDataDictionary viewData, Boolean excludePropertyErrors)
   в Microsoft.AspNetCore.Mvc.ViewFeatures.DefaultHtmlGenerator.GenerateValidationSummary(ViewContext viewContext, Boolean excludePropertyErrors, String message, String headerTag, Object htmlAttributes)
   в Microsoft.AspNetCore.Mvc.ViewFeatures.HtmlHelper.GenerateValidationSummary(Boolean excludePropertyErrors, String message, Object htmlAttributes, String tag)
   в Microsoft.AspNetCore.Mvc.ViewFeatures.HtmlHelper.ValidationSummary(Boolean excludePropertyErrors, String message, Object htmlAttributes, String tag)
   в Microsoft.AspNetCore.Mvc.Rendering.HtmlHelperValidationExtensions.ValidationSummary(IHtmlHelper htmlHelper)

[dougbu]

We definitely test w/ ValidationSummary.All. This issue is likely specific to your model types. Please share those class definitions.

[rsheptolut]

@dougbu No, nothing specific to a model, this fails on all my models. I feed EF6 objects directly to the views, by the way. Such is life.

Example (simplified, but verified):

[Table("Currency", Schema = "dic")]
public class Currency
{
    [Timestamp]
    [Column(Order = int.MaxValue)]
    public byte[] Ts { get; set; }

    [Key]
    [StringLength(3, MinimumLength = 3)]
    [Column(TypeName = "nchar")]
    public string Id { get; set; }

    [StringLength(3)]
    public string CurrencySymbol { get; set; }
}

public class CurrencyController
{
    [ValidateAntiForgeryToken]
    [HttpPost]
    [ActionName("Edit")]
    public IActionResult ApplyEdit(Currency model)
    {
        ModelState.AddModelError(nameof(model.CurrencySymbol), "Lame!");
        return View(model);
    }
}

Currency/Edit.cshtml (simplified, I posted values to it via refreshing browser which remembers 'real' post values)

@model object
@Html.ValidationSummary();

Debugger says that Model is of type "Currency", so is ModelMetadata.ModelType == typeof(Currency), so everything seems legit. And my other 100 tons of code that depend heavily on ModelMetadata continue to work perfectly.

[dougbu]

Looks like a straightforward bug in ValidationHelpers.Visit(). That method (specifically this block) doesn't handle cases where a collection property is not bound. Just needs a null check on modelStateEntry.Children.

[dougbu]

Reassigning to do the straightforward fix.

[pranavkm]

@dougbu is there a workaround for this in 1.0.0 (besides the option @rsheptolut suggested)?