DictionaryBasedValueProvider results null when value is not found

* Guard against Dictionary returning null values

src/Microsoft.AspNet.Mvc.ModelBinding/ValueProviders/DictionaryBasedValueProvider.cs

@@ -21,13 +21,18 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
         public Task<ValueProviderResult> GetValueAsync([NotNull] string key)
         {
             object value;
+            ValueProviderResult result;
             if (_values.TryGetValue(key, out value))
             {
-                var result = new ValueProviderResult(value, value.ToString(), CultureInfo.InvariantCulture);
+                var attemptedValue = value != null ? value.ToString() : null;
-                return Task.FromResult(result);
+                result = new ValueProviderResult(value, attemptedValue, CultureInfo.InvariantCulture);
             }
-
+            else
-            return null;
+            {
+                result = null;
+            }
+            
+            return Task.FromResult(result);
         }
     }
 }

test/Microsoft.AspNet.Mvc.ModelBinding.Test/ValueProviders/DictionaryBasedValueProviderTests.cs

@@ -0,0 +1,97 @@
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using Xunit;
+
+namespace Microsoft.AspNet.Mvc.ModelBinding
+{
+    public class DictionaryBasedValueProviderTestss
+    {
+        [Fact]
+        public async Task GetValueProvider_ReturnsNull_WhenKeyIsNotFound()
+        {
+            // Arrange
+            var values = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase)
+            {
+                { "test-key", "value" }
+            };
+            var provider = new DictionaryBasedValueProvider(values);
+            
+            // Act
+            var result = await provider.GetValueAsync("not-test-key");
+
+            // Assert
+            Assert.Null(result);
+        }
+
+        [Fact]
+        public async Task GetValueProvider_ReturnsValue_IfKeyIsPresent()
+        {
+            // Arrange
+            var values = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase)
+            {
+                { "test-key", "test-value" }
+            };
+            var provider = new DictionaryBasedValueProvider(values);
+
+            // Act
+            var result = await provider.GetValueAsync("test-key");
+
+            // Assert
+            Assert.Equal("test-value", result.RawValue);
+        }
+
+        [Fact]
+        public async Task ContainsPrefixAsync_ReturnsNullValue_IfKeyIsPresent()
+        {
+            // Arrange
+            var values = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase)
+            {
+                { "test-key", null }
+            };
+            var provider = new DictionaryBasedValueProvider(values);
+
+            // Act
+            var result = await provider.GetValueAsync("test-key");
+
+            // Assert
+            Assert.NotNull(result);
+            Assert.Null(result.RawValue);
+            Assert.Null(result.AttemptedValue);
+        }
+
+        [Fact]
+        public async Task ContainsPrefixAsync_ReturnsFalse_IfKeyIsNotPresent()
+        {
+            // Arrange
+            var values = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase)
+            {
+                { "test-key", "test-value" }
+            };
+            var provider = new DictionaryBasedValueProvider(values);
+
+            // Act
+            var result = await provider.ContainsPrefixAsync("not-test-key");
+
+            // Assert
+            Assert.False(result);
+        }
+
+        [Fact]
+        public async Task ContainsPrefixAsync_ReturnsTrue_IfKeyIsPresent()
+        {
+            // Arrange
+            var values = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase)
+            {
+                { "test-key", "test-value" }
+            };
+            var provider = new DictionaryBasedValueProvider(values);
+
+            // Act
+            var result = await provider.ContainsPrefixAsync("test-key");
+
+            // Assert
+            Assert.True(result);
+        }
+    }
+}