Add `null` checks for MVC tag helpers

src/Microsoft.AspNet.Mvc.Razor/TagHelpers/UrlResolutionTagHelper.cs

@@ -6,7 +6,6 @@ using System.Collections.Generic;
 using System.ComponentModel;
 using System.Reflection;
 using Microsoft.AspNet.Mvc.Rendering;
-using Microsoft.AspNet.Mvc.Routing;
 using Microsoft.AspNet.Razor.Runtime.TagHelpers;
 using Microsoft.Extensions.WebEncoders;
 
@@ -108,6 +107,16 @@ namespace Microsoft.AspNet.Mvc.Razor.TagHelpers
         /// <inheritdoc />
         public override void Process(TagHelperContext context, TagHelperOutput output)
         {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            if (output == null)
+            {
+                throw new ArgumentNullException(nameof(output));
+            }
+
             IEnumerable<string> attributeNames;
             if (ElementAttributeLookups.TryGetValue(output.TagName, out attributeNames))
             {
@@ -130,6 +139,16 @@ namespace Microsoft.AspNet.Mvc.Razor.TagHelpers
         /// <param name="output">The <see cref="TagHelperOutput"/>.</param>
         protected void ProcessUrlAttribute(string attributeName, TagHelperOutput output)
         {
+            if (attributeName == null)
+            {
+                throw new ArgumentNullException(nameof(attributeName));
+            }
+
+            if (output == null)
+            {
+                throw new ArgumentNullException(nameof(output));
+            }
+
             IEnumerable<TagHelperAttribute> attributes;
             if (output.Attributes.TryGetAttributes(attributeName, out attributes))
             {

src/Microsoft.AspNet.Mvc.TagHelpers/AnchorTagHelper.cs

@@ -111,6 +111,16 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
         /// </exception>
         public override void Process(TagHelperContext context, TagHelperOutput output)
         {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            if (output == null)
+            {
+                throw new ArgumentNullException(nameof(output));
+            }
+
             // If "href" is already set, it means the user is attempting to use a normal anchor.
             if (output.Attributes.ContainsName(Href))
             {

src/Microsoft.AspNet.Mvc.TagHelpers/CacheTagHelper.cs

@@ -138,6 +138,16 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
         /// <inheritdoc />
         public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
         {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            if (output == null)
+            {
+                throw new ArgumentNullException(nameof(output));
+            }
+
             TagHelperContent result = null;
             if (Enabled)
             {

src/Microsoft.AspNet.Mvc.TagHelpers/EnvironmentTagHelper.cs

@@ -48,6 +48,16 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
         /// <inheritdoc />
         public override void Process(TagHelperContext context, TagHelperOutput output)
         {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            if (output == null)
+            {
+                throw new ArgumentNullException(nameof(output));
+            }
+
             // Always strip the outer tag name as we never want <environment> to render
             output.TagName = null;
 
@@ -80,7 +90,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                 // Matching environment name found, do nothing
                 return;
             }
-            
+
             // No matching environment name found, suppress all output
             output.SuppressOutput();
         }

src/Microsoft.AspNet.Mvc.TagHelpers/FormTagHelper.cs

@@ -99,6 +99,16 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
         /// </exception>
         public override void Process(TagHelperContext context, TagHelperOutput output)
         {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            if (output == null)
+            {
+                throw new ArgumentNullException(nameof(output));
+            }
+
             var antiforgeryDefault = true;
 
             // If "action" is already set, it means the user is attempting to use a normal <form>.

src/Microsoft.AspNet.Mvc.TagHelpers/ImageTagHelper.cs

@@ -1,10 +1,10 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
 using Microsoft.AspNet.Hosting;
 using Microsoft.AspNet.Mvc.Razor.TagHelpers;
 using Microsoft.AspNet.Mvc.Rendering;
-using Microsoft.AspNet.Mvc.Routing;
 using Microsoft.AspNet.Mvc.TagHelpers.Internal;
 using Microsoft.AspNet.Mvc.ViewFeatures;
 using Microsoft.AspNet.Razor.Runtime.TagHelpers;
@@ -87,6 +87,16 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
         /// <inheritdoc />
         public override void Process(TagHelperContext context, TagHelperOutput output)
         {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            if (output == null)
+            {
+                throw new ArgumentNullException(nameof(output));
+            }
+
             output.CopyHtmlAttribute(SrcAttributeName, context);
             ProcessUrlAttribute(SrcAttributeName, output);
 

src/Microsoft.AspNet.Mvc.TagHelpers/InputTagHelper.cs

@@ -133,6 +133,16 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
         /// </exception>
         public override void Process(TagHelperContext context, TagHelperOutput output)
         {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            if (output == null)
+            {
+                throw new ArgumentNullException(nameof(output));
+            }
+
             // Pass through attributes that are also well-known HTML attributes. Must be done prior to any copying
             // from a TagBuilder.
             if (InputTypeName != null)

src/Microsoft.AspNet.Mvc.TagHelpers/LabelTagHelper.cs

@@ -1,6 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Mvc.Rendering;
 using Microsoft.AspNet.Mvc.ViewFeatures;
@@ -50,6 +51,16 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
         /// <remarks>Does nothing if <see cref="For"/> is <c>null</c>.</remarks>
         public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
         {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            if (output == null)
+            {
+                throw new ArgumentNullException(nameof(output));
+            }
+
             var tagBuilder = Generator.GenerateLabel(
                 ViewContext,
                 For.ModelExplorer,

src/Microsoft.AspNet.Mvc.TagHelpers/LinkTagHelper.cs

@@ -8,7 +8,6 @@ using System.Linq;
 using Microsoft.AspNet.Hosting;
 using Microsoft.AspNet.Mvc.Razor.TagHelpers;
 using Microsoft.AspNet.Mvc.Rendering;
-using Microsoft.AspNet.Mvc.Routing;
 using Microsoft.AspNet.Mvc.TagHelpers.Internal;
 using Microsoft.AspNet.Mvc.ViewFeatures;
 using Microsoft.AspNet.Razor.Runtime.TagHelpers;
@@ -217,7 +216,15 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
         /// <inheritdoc />
         public override void Process(TagHelperContext context, TagHelperOutput output)
         {
-            string resolvedUrl;
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            if (output == null)
+            {
+                throw new ArgumentNullException(nameof(output));
+            }
 
             // Pass through attribute that is also a well-known HTML attribute.
             if (Href != null)
@@ -274,6 +281,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
 
             if (mode == Mode.Fallback)
             {
+                string resolvedUrl;
                 if (TryResolveUrl(FallbackHref, encodeWebRoot: false, resolvedUrl: out resolvedUrl))
                 {
                     FallbackHref = resolvedUrl;

src/Microsoft.AspNet.Mvc.TagHelpers/OptionTagHelper.cs

@@ -61,6 +61,16 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
         /// </remarks>
         public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
         {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            if (output == null)
+            {
+                throw new ArgumentNullException(nameof(output));
+            }
+
             // Pass through attributes that are also well-known HTML attributes.
             if (Value != null)
             {

src/Microsoft.AspNet.Mvc.TagHelpers/ScriptTagHelper.cs

@@ -7,7 +7,6 @@ using System.Linq;
 using Microsoft.AspNet.Hosting;
 using Microsoft.AspNet.Mvc.Razor.TagHelpers;
 using Microsoft.AspNet.Mvc.Rendering;
-using Microsoft.AspNet.Mvc.Routing;
 using Microsoft.AspNet.Mvc.TagHelpers.Internal;
 using Microsoft.AspNet.Mvc.ViewFeatures;
 using Microsoft.AspNet.Razor.Runtime.TagHelpers;
@@ -185,7 +184,15 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
         /// <inheritdoc />
         public override void Process(TagHelperContext context, TagHelperOutput output)
         {
-            string resolvedUrl;
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            if (output == null)
+            {
+                throw new ArgumentNullException(nameof(output));
+            }
 
             // Pass through attribute that is also a well-known HTML attribute.
             if (Src != null)
@@ -242,6 +249,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
 
             if (mode == Mode.Fallback)
             {
+                string resolvedUrl;
                 if (TryResolveUrl(FallbackSrc, encodeWebRoot: false, resolvedUrl: out resolvedUrl))
                 {
                     FallbackSrc = resolvedUrl;

src/Microsoft.AspNet.Mvc.TagHelpers/SelectTagHelper.cs

@@ -76,6 +76,16 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
         /// </exception>
         public override void Process(TagHelperContext context, TagHelperOutput output)
         {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            if (output == null)
+            {
+                throw new ArgumentNullException(nameof(output));
+            }
+
             // Note null or empty For.Name is allowed because TemplateInfo.HtmlFieldPrefix may be sufficient.
             // IHtmlGenerator will enforce name requirements.
             var metadata = For.Metadata;

src/Microsoft.AspNet.Mvc.TagHelpers/TextAreaTagHelper.cs

@@ -1,6 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
 using Microsoft.AspNet.Mvc.Rendering;
 using Microsoft.AspNet.Mvc.ViewFeatures;
 using Microsoft.AspNet.Razor.Runtime.TagHelpers;
@@ -49,6 +50,16 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
         /// <remarks>Does nothing if <see cref="For"/> is <c>null</c>.</remarks>
         public override void Process(TagHelperContext context, TagHelperOutput output)
         {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            if (output == null)
+            {
+                throw new ArgumentNullException(nameof(output));
+            }
+
             var tagBuilder = Generator.GenerateTextArea(
                 ViewContext,
                 For.ModelExplorer,

src/Microsoft.AspNet.Mvc.TagHelpers/ValidationMessageTagHelper.cs

@@ -1,6 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Mvc.Rendering;
 using Microsoft.AspNet.Mvc.ViewFeatures;
@@ -51,6 +52,16 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
         /// <remarks>Does nothing if <see cref="For"/> is <c>null</c>.</remarks>
         public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
         {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            if (output == null)
+            {
+                throw new ArgumentNullException(nameof(output));
+            }
+
             if (For != null)
             {
                 var tagBuilder = Generator.GenerateValidationMessage(ViewContext,

src/Microsoft.AspNet.Mvc.TagHelpers/ValidationSummaryTagHelper.cs

@@ -83,6 +83,16 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
         /// <remarks>Does nothing if <see cref="ValidationSummary"/> is <see cref="ValidationSummary.None"/>.</remarks>
         public override void Process(TagHelperContext context, TagHelperOutput output)
         {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            if (output == null)
+            {
+                throw new ArgumentNullException(nameof(output));
+            }
+
             if (ValidationSummary == ValidationSummary.None)
             {
                 return;

test/Microsoft.AspNet.Mvc.Razor.Test/TagHelpers/UrlResolutionTagHelperTest.cs

@@ -2,9 +2,11 @@
 // 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.Linq;
 using System.Reflection;
+using System.Threading.Tasks;
 using Microsoft.AspNet.Mvc.Rendering;
-using Microsoft.AspNet.Mvc.Routing;
 using Microsoft.AspNet.Razor.Runtime.TagHelpers;
 using Microsoft.Extensions.WebEncoders;
 using Moq;
@@ -57,8 +59,15 @@ namespace Microsoft.AspNet.Mvc.Razor.TagHelpers
                 .Returns(new Func<string, string>(value => "/approot" + value.Substring(1)));
             var tagHelper = new UrlResolutionTagHelper(urlHelperMock.Object, new TestHtmlEncoder());
 
+            var context = new TagHelperContext(
+                allAttributes: new ReadOnlyTagHelperAttributeList<IReadOnlyTagHelperAttribute>(
+                    Enumerable.Empty<IReadOnlyTagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test",
+                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+
             // Act
-            tagHelper.Process(context: null, output: tagHelperOutput);
+            tagHelper.Process(context, tagHelperOutput);
 
             // Assert
             var attribute = Assert.Single(tagHelperOutput.Attributes);
@@ -106,8 +115,15 @@ namespace Microsoft.AspNet.Mvc.Razor.TagHelpers
                 .Returns("approot/home/index.html");
             var tagHelper = new UrlResolutionTagHelper(urlHelperMock.Object, htmlEncoder: null);
 
+            var context = new TagHelperContext(
+                allAttributes: new ReadOnlyTagHelperAttributeList<IReadOnlyTagHelperAttribute>(
+                    Enumerable.Empty<IReadOnlyTagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test",
+                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+
             // Act
-            tagHelper.Process(context: null, output: tagHelperOutput);
+            tagHelper.Process(context, tagHelperOutput);
 
             // Assert
             var attribute = Assert.Single(tagHelperOutput.Attributes);
@@ -128,8 +144,15 @@ namespace Microsoft.AspNet.Mvc.Razor.TagHelpers
                 });
             var tagHelper = new UrlResolutionTagHelper(urlHelper: null, htmlEncoder: null);
 
+            var context = new TagHelperContext(
+                allAttributes: new ReadOnlyTagHelperAttributeList<IReadOnlyTagHelperAttribute>(
+                    Enumerable.Empty<IReadOnlyTagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test",
+                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+
             // Act
-            tagHelper.Process(context: null, output: tagHelperOutput);
+            tagHelper.Process(context, tagHelperOutput);
 
             // Assert
             var attribute = Assert.Single(tagHelperOutput.Attributes);
@@ -162,9 +185,16 @@ namespace Microsoft.AspNet.Mvc.Razor.TagHelpers
                 .Returns("UnexpectedResult");
             var tagHelper = new UrlResolutionTagHelper(urlHelperMock.Object, htmlEncoder: null);
 
+            var context = new TagHelperContext(
+                allAttributes: new ReadOnlyTagHelperAttributeList<IReadOnlyTagHelperAttribute>(
+                    Enumerable.Empty<IReadOnlyTagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test",
+                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+
             // Act & Assert
             var exception = Assert.Throws<InvalidOperationException>(
-                () => tagHelper.Process(context: null, output: tagHelperOutput));
+                () => tagHelper.Process(context, tagHelperOutput));
             Assert.Equal(expectedExceptionMessage, exception.Message, StringComparer.Ordinal);
         }
     }

test/Microsoft.AspNet.Mvc.TagHelpers.Test/AnchorTagHelperTest.cs

@@ -10,7 +10,6 @@ using Microsoft.AspNet.Mvc.Rendering;
 using Microsoft.AspNet.Mvc.Routing;
 using Microsoft.AspNet.Mvc.ViewFeatures;
 using Microsoft.AspNet.Razor.Runtime.TagHelpers;
-using Microsoft.Extensions.WebEncoders.Testing;
 using Moq;
 using Xunit;
 
@@ -220,9 +219,16 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                                        "'asp-action', 'asp-controller', 'asp-route', 'asp-protocol', 'asp-host', or " +
                                        "'asp-fragment' attribute.";
 
+            var context = new TagHelperContext(
+                allAttributes: new ReadOnlyTagHelperAttributeList<IReadOnlyTagHelperAttribute>(
+                    Enumerable.Empty<IReadOnlyTagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test",
+                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+
             // Act & Assert
             var ex = await Assert.ThrowsAsync<InvalidOperationException>(
-                () => anchorTagHelper.ProcessAsync(context: null, output: output));
+                () => anchorTagHelper.ProcessAsync(context, output));
 
             Assert.Equal(expectedErrorMessage, ex.Message);
         }
@@ -248,9 +254,16 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var expectedErrorMessage = "Cannot determine an 'href' attribute for <a>. An <a> with a specified " +
                 "'asp-route' must not have an 'asp-action' or 'asp-controller' attribute.";
 
+            var context = new TagHelperContext(
+                allAttributes: new ReadOnlyTagHelperAttributeList<IReadOnlyTagHelperAttribute>(
+                    Enumerable.Empty<IReadOnlyTagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test",
+                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+
             // Act & Assert
             var ex = await Assert.ThrowsAsync<InvalidOperationException>(
-                () => anchorTagHelper.ProcessAsync(context: null, output: output));
+                () => anchorTagHelper.ProcessAsync(context, output));
 
             Assert.Equal(expectedErrorMessage, ex.Message);
         }

test/Microsoft.AspNet.Mvc.TagHelpers.Test/FormTagHelperTest.cs

@@ -407,9 +407,16 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                                        "'action' must not have attributes starting with 'asp-route-' or an " +
                                        "'asp-action' or 'asp-controller' or 'asp-route' attribute.";
 
+            var context = new TagHelperContext(
+                allAttributes: new ReadOnlyTagHelperAttributeList<IReadOnlyTagHelperAttribute>(
+                    Enumerable.Empty<IReadOnlyTagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test",
+                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+
             // Act & Assert
             var ex = await Assert.ThrowsAsync<InvalidOperationException>(
-                () => formTagHelper.ProcessAsync(context: null, output: tagHelperOutput));
+                () => formTagHelper.ProcessAsync(context, tagHelperOutput));
 
             Assert.Equal(expectedErrorMessage, ex.Message);
         }
@@ -431,9 +438,16 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var expectedErrorMessage = "Cannot determine an 'action' attribute for <form>. A <form> with a specified " +
                 "'asp-route' must not have an 'asp-action' or 'asp-controller' attribute.";
 
+            var context = new TagHelperContext(
+                allAttributes: new ReadOnlyTagHelperAttributeList<IReadOnlyTagHelperAttribute>(
+                    Enumerable.Empty<IReadOnlyTagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test",
+                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+
             // Act & Assert
             var ex = await Assert.ThrowsAsync<InvalidOperationException>(
-                () => formTagHelper.ProcessAsync(context: null, output: output));
+                () => formTagHelper.ProcessAsync(context, output));
 
             Assert.Equal(expectedErrorMessage, ex.Message);
         }

test/Microsoft.AspNet.Mvc.TagHelpers.Test/ValidationMessageTagHelperTest.cs

@@ -62,7 +62,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             output.PreContent.SetContent(expectedPreContent);
             output.Content.SetContent(expectedContent);
             output.PostContent.SetContent(expectedPostContent);
-            
+
             var viewContext = TestableHtmlGenerator.GetViewContext(model: null,
                                                                    htmlGenerator: htmlGenerator,
                                                                    metadataProvider: metadataProvider);
@@ -127,7 +127,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             validationMessageTagHelper.ViewContext = expectedViewContext;
 
             // Act & Assert
-            await validationMessageTagHelper.ProcessAsync(context, output: output);
+            await validationMessageTagHelper.ProcessAsync(context, output);
 
             generator.Verify();
             Assert.Equal("span", output.TagName);
@@ -185,7 +185,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             validationMessageTagHelper.ViewContext = viewContext;
 
             // Act
-            await validationMessageTagHelper.ProcessAsync(context, output: output);
+            await validationMessageTagHelper.ProcessAsync(context, output);
 
             // Assert
             Assert.Equal("span", output.TagName);
@@ -243,7 +243,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             validationMessageTagHelper.ViewContext = viewContext;
 
             // Act
-            await validationMessageTagHelper.ProcessAsync(context, output: output);
+            await validationMessageTagHelper.ProcessAsync(context, output);
 
             // Assert
             Assert.Equal("span", output.TagName);
@@ -271,11 +271,18 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             output.Content.SetContent(expectedContent);
             output.PostContent.SetContent(expectedPostContent);
 
+            var context = new TagHelperContext(
+                allAttributes: new ReadOnlyTagHelperAttributeList<IReadOnlyTagHelperAttribute>(
+                    Enumerable.Empty<IReadOnlyTagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test",
+                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+
             var viewContext = CreateViewContext();
             validationMessageTagHelper.ViewContext = viewContext;
 
             // Act
-            await validationMessageTagHelper.ProcessAsync(context: null, output: output);
+            await validationMessageTagHelper.ProcessAsync(context, output);
 
             // Assert
             Assert.Equal("span", output.TagName);

test/Microsoft.AspNet.Mvc.TagHelpers.Test/ValidationSummaryTagHelperTest.cs

@@ -115,11 +115,17 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             output.Content.SetContent(expectedContent);
             output.PostContent.SetContent(expectedPostContent);
 
-            
             validationSummaryTagHelper.ViewContext = expectedViewContext;
 
+            var context = new TagHelperContext(
+                allAttributes: new ReadOnlyTagHelperAttributeList<IReadOnlyTagHelperAttribute>(
+                    Enumerable.Empty<IReadOnlyTagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test",
+                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+
             // Act & Assert
-            await validationSummaryTagHelper.ProcessAsync(context: null, output: output);
+            await validationSummaryTagHelper.ProcessAsync(context, output);
 
             generator.Verify();
             Assert.Equal("div", output.TagName);
@@ -166,8 +172,15 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var viewContext = CreateViewContext();
             validationSummaryTagHelper.ViewContext = viewContext;
 
+            var context = new TagHelperContext(
+                allAttributes: new ReadOnlyTagHelperAttributeList<IReadOnlyTagHelperAttribute>(
+                    Enumerable.Empty<IReadOnlyTagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test",
+                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+
             // Act
-            await validationSummaryTagHelper.ProcessAsync(context: null, output: output);
+            await validationSummaryTagHelper.ProcessAsync(context, output);
 
             // Assert
             Assert.Equal("div", output.TagName);
@@ -207,8 +220,15 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var viewContext = CreateViewContext();
             validationSummaryTagHelper.ViewContext = viewContext;
 
+            var context = new TagHelperContext(
+                allAttributes: new ReadOnlyTagHelperAttributeList<IReadOnlyTagHelperAttribute>(
+                    Enumerable.Empty<IReadOnlyTagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test",
+                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+
             // Act
-            await validationSummaryTagHelper.ProcessAsync(context: null, output: output);
+            await validationSummaryTagHelper.ProcessAsync(context, output);
 
             // Assert
             Assert.Equal("div", output.TagName);
@@ -255,8 +275,15 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var viewContext = CreateViewContext();
             validationSummaryTagHelper.ViewContext = viewContext;
 
+            var context = new TagHelperContext(
+                allAttributes: new ReadOnlyTagHelperAttributeList<IReadOnlyTagHelperAttribute>(
+                    Enumerable.Empty<IReadOnlyTagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test",
+                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+
             // Act
-            await validationSummaryTagHelper.ProcessAsync(context: null, output: output);
+            await validationSummaryTagHelper.ProcessAsync(context, output);
 
             // Assert
             Assert.Equal("div", output.TagName);