Address PR comments

- add single-parameter `ValueProviderResult` constructor
 - use in most of the greedy and type-matching model binders
- revert changes to `FormCollectionModelBinder` and related tests
 - do _not_ add a `ModelState` entry in this binder
- add doc comments in `ValueProviderResult` class
- simplify logic in `FormFileModelBinder`
 - exit early instead of using `typeMatched` variable

nits:
- use new `ValueProviderResult` constructor in many existing tests
- `""` -> `string.Empty` and `vpr` -> `valueProviderResult` in `ValueProviderResultTest`
- improve some test names in `BodyValidationIntegrationTests`
- do not check `Message` of a Json.NET `Exception`

src/Microsoft.AspNet.Mvc.Abstractions/ModelBinding/ValueProviderResult.cs

@@ -12,25 +12,59 @@
 
 namespace Microsoft.AspNet.Mvc.ModelBinding
 {
+    /// <summary>
+    /// Result of an <see cref="IValueProvider.GetValueAsync"/> operation.
+    /// </summary>
     public class ValueProviderResult
     {
         private static readonly CultureInfo _staticCulture = CultureInfo.InvariantCulture;
         private CultureInfo _instanceCulture;
 
-        // default constructor so that subclassed types can set the properties themselves
+        /// <summary>
+        /// Instantiates a new instance of the <see cref="ValueProviderResult"/> class. Subclass must at least set
+        /// <see cref="Culture"/> to avoid <see cref="Exception"/>s in <see cref="ConvertTo(Type, CultureInfo)"/>.
+        /// </summary>
         protected ValueProviderResult()
         {
         }
 
+        /// <summary>
+        /// Instantiates a new instance of the <see cref="ValueProviderResult"/> class with given
+        /// <paramref name="rawValue"/>. Initializes <see cref="Culture"/> to
+        /// <see cref="CultureInfo.InvariantCulture"/>.
+        /// </summary>
+        /// <param name="rawValue">The <see cref="RawValue"/> value of the new instance.</param>
+        public ValueProviderResult(object rawValue)
+            : this(rawValue, attemptedValue: null, culture: _staticCulture)
+        {
+        }
+
+        /// <summary>
+        /// Instantiates a new instance of the <see cref="ValueProviderResult"/> class with given
+        /// <paramref name="rawValue"/>, <paramref name="attemptedValue"/>, and <paramref name="culture"/>.
+        /// </summary>
+        /// <param name="rawValue">The <see cref="RawValue"/> value of the new instance.</param>
+        /// <param name="attemptedValue">The <see cref="AttemptedValue"/> value of the new instance.</param>
+        /// <param name="culture">The <see cref="Culture"/> value of the new instance.</param>
         public ValueProviderResult(object rawValue, string attemptedValue, CultureInfo culture)
         {
             RawValue = rawValue;
             AttemptedValue = attemptedValue;
             Culture = culture;
         }
 
+        /// <summary>
+        /// <see cref="string"/> conversion of <see cref="RawValue"/>.
+        /// </summary>
+        /// <remarks>
+        /// Used in helpers that generate <c>&lt;textarea&gt;</c> elements as well as some error messages.
+        /// </remarks>
         public string AttemptedValue { get; protected set; }
 
+        /// <summary>
+        /// <see cref="CultureInfo"/> to use in <see cref="ConvertTo(Type)"/> or
+        /// <see cref="ConvertTo(Type, CultureInfo)"/> if passed <see cref="CultureInfo"/> is <c>null</c>.
+        /// </summary>
         public CultureInfo Culture
         {
             get
@@ -44,13 +78,37 @@ public CultureInfo Culture
             protected set { _instanceCulture = value; }
         }
 
+        /// <summary>
+        /// The provided <see cref="object"/>.
+        /// </summary>
         public object RawValue { get; protected set; }
 
+        /// <summary>
+        /// Converts <see cref="RawValue"/> to the given <paramref name="type"/>. Uses <see cref="Culture"/> for
+        /// <see cref="TypeConverter"/> operations.
+        /// </summary>
+        /// <param name="type">The target <see cref="Type"/> of the conversion.</param>
+        /// <returns>
+        /// <see cref="RawValue"/> converted to the given <paramref name="type"/>. <c>null</c> if the conversion fails.
+        /// </returns>
         public object ConvertTo(Type type)
         {
             return ConvertTo(type, culture: null);
         }
 
+        /// <summary>
+        /// Converts <see cref="RawValue"/> to the given <paramref name="type"/> using the given
+        /// <paramref name="culture"/>.
+        /// </summary>
+        /// <param name="type">The target <see cref="Type"/> of the conversion.</param>
+        /// <param name="culture">
+        /// The <see cref="CultureInfo"/> to use for <see cref="TypeConverter"/> operations. Uses
+        /// <see cref="Culture"/> if this parameter is <c>null</c>.
+        /// </param>
+        /// <returns>
+        /// <see cref="RawValue"/> converted to the given <paramref name="type"/> using the given
+        /// <paramref name="culture"/>. <c>null</c> if the conversion fails.
+        /// </returns>
         public virtual object ConvertTo([NotNull] Type type, CultureInfo culture)
         {
             var value = RawValue;

src/Microsoft.AspNet.Mvc.Core/ModelBinding/BodyModelBinder.cs

@@ -66,7 +66,7 @@ protected async override Task<ModelBindingResult> BindModelCoreAsync(
                     return new ModelBindingResult(modelBindingKey);
                 }
 
-                var valueProviderResult = new ValueProviderResult(model, attemptedValue: null, culture: null);
+                var valueProviderResult = new ValueProviderResult(rawValue: model);
                 bindingContext.ModelState.SetModelValue(modelBindingKey, valueProviderResult);
 
                 var validationNode = new ModelValidationNode(modelBindingKey, bindingContext.ModelMetadata, model)

src/Microsoft.AspNet.Mvc.Core/ModelBinding/FormCollectionModelBinder.cs

@@ -25,7 +25,7 @@ public async Task<ModelBindingResult> BindModelAsync([NotNull] ModelBindingConte
                 return null;
             }
 
-            object model;
+            object model = null;
             var request = bindingContext.OperationBindingContext.HttpContext.Request;
             if (request.HasFormContentType)
             {
@@ -45,9 +45,6 @@ public async Task<ModelBindingResult> BindModelAsync([NotNull] ModelBindingConte
                 model = new FormCollection(new Dictionary<string, string[]>());
             }
 
-            var valueProviderResult = new ValueProviderResult(model, attemptedValue: null, culture: null);
-            bindingContext.ModelState.SetModelValue(bindingContext.ModelName, valueProviderResult);
-
             var validationNode =
                  new ModelValidationNode(bindingContext.ModelName, bindingContext.ModelMetadata, model);
             return new ModelBindingResult(

src/Microsoft.AspNet.Mvc.Core/ModelBinding/FormFileModelBinder.cs

@@ -22,41 +22,38 @@ public class FormFileModelBinder : IModelBinder
         /// <inheritdoc />
         public async Task<ModelBindingResult> BindModelAsync([NotNull] ModelBindingContext bindingContext)
         {
-            var typeMatched = false;
-            object value = null;
+            object value;
             if (bindingContext.ModelType == typeof(IFormFile))
             {
-                typeMatched = true;
                 var postedFiles = await GetFormFilesAsync(bindingContext);
                 value = postedFiles.FirstOrDefault();
             }
             else if (typeof(IEnumerable<IFormFile>).IsAssignableFrom(bindingContext.ModelType))
             {
-                typeMatched = true;
                 var postedFiles = await GetFormFilesAsync(bindingContext);
                 value = ModelBindingHelper.ConvertValuesToCollectionType(bindingContext.ModelType, postedFiles);
             }
-
-            if (typeMatched)
+            else
             {
-                ModelValidationNode validationNode = null;
-                if (value != null)
-                {
-                    validationNode =
-                        new ModelValidationNode(bindingContext.ModelName, bindingContext.ModelMetadata, value);
+                // This binder does not support the requested type.
+                return null;
+            }
 
-                    var valueProviderResult = new ValueProviderResult(value, attemptedValue: null, culture: null);
-                    bindingContext.ModelState.SetModelValue(bindingContext.ModelName, valueProviderResult);
-                }
+            ModelValidationNode validationNode = null;
+            if (value != null)
+            {
+                validationNode =
+                    new ModelValidationNode(bindingContext.ModelName, bindingContext.ModelMetadata, value);
 
-                return new ModelBindingResult(
-                    value,
-                    bindingContext.ModelName,
-                    isModelSet: value != null,
-                    validationNode: validationNode);
+                var valueProviderResult = new ValueProviderResult(rawValue: value);
+                bindingContext.ModelState.SetModelValue(bindingContext.ModelName, valueProviderResult);
             }
 
-            return null;
+            return new ModelBindingResult(
+                value,
+                bindingContext.ModelName,
+                isModelSet: value != null,
+                validationNode: validationNode);
         }
 
         private async Task<List<IFormFile>> GetFormFilesAsync(ModelBindingContext bindingContext)

src/Microsoft.AspNet.Mvc.Core/ModelBinding/HeaderModelBinder.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System.Collections.Generic;
+using System.Globalization;
 #if DNXCORE50
 using System.Reflection;
 #endif
@@ -61,7 +62,7 @@ protected override Task<ModelBindingResult> BindModelCoreAsync([NotNull] ModelBi
                     model);
 
                 var attemptedValue = (model as string) ?? request.Headers.Get(headerName);
-                var valueProviderResult = new ValueProviderResult(model, attemptedValue, culture: null);
+                var valueProviderResult = new ValueProviderResult(model, attemptedValue, CultureInfo.InvariantCulture);
                 bindingContext.ModelState.SetModelValue(bindingContext.ModelName, valueProviderResult);
             }
 

test/Microsoft.AspNet.Mvc.Abstractions.Test/ModelBinding/ModelStateDictionaryTest.cs

@@ -2,7 +2,6 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
 using System.Globalization;
 using Microsoft.Framework.Internal;
 using Xunit;
@@ -75,7 +74,7 @@ public void MarkFieldSkipped_Throws_IfStateIsInvalid()
 
             // Act
             var exception = Assert.Throws<InvalidOperationException>(() => source.MarkFieldSkipped("key"));
-            
+
             // Assert
             Assert.Equal(
                 "A field previously marked invalid should not be marked skipped.",
@@ -138,7 +137,7 @@ public void MarkFieldValid_Throws_IfStateIsInvalid()
 
             // Act
             var exception = Assert.Throws<InvalidOperationException>(() => source.MarkFieldValid("key"));
-            
+
             // Assert
             Assert.Equal(
                 "A field previously marked invalid should not be marked valid.",
@@ -278,7 +277,7 @@ public void GetFieldValidationState_ReturnsValidIfModelStateDoesNotContainErrors
             // Arrange
             var validState = new ModelState
             {
-                Value = new ValueProviderResult(null, null, null),
+                Value = new ValueProviderResult(rawValue: null),
                 ValidationState = ModelValidationState.Valid
             };
             var msd = new ModelStateDictionary
@@ -317,7 +316,7 @@ public void GetFieldValidationState_IndexedPrefix_ReturnsValidIfModelStateDoesNo
             // Arrange
             var validState = new ModelState
             {
-                Value = new ValueProviderResult(null, null, null),
+                Value = new ValueProviderResult(rawValue: null),
                 ValidationState = ModelValidationState.Valid
             };
             var msd = new ModelStateDictionary