[Fixes #6943] Unit Testing Page Model Throws Null Ref On ModelState check

src/Microsoft.AspNetCore.Mvc.Core/ControllerBase.cs

@@ -56,7 +56,7 @@ namespace Microsoft.AspNetCore.Mvc
         /// <summary>
         /// Gets the <see cref="ModelStateDictionary"/> that contains the state of the model and of model-binding validation.
         /// </summary>
-        public ModelStateDictionary ModelState => ControllerContext?.ModelState;
+        public ModelStateDictionary ModelState => ControllerContext.ModelState;
 
         /// <summary>
         /// Gets or sets the <see cref="Mvc.ControllerContext"/>.

src/Microsoft.AspNetCore.Mvc.RazorPages/PageModel.cs

@@ -30,17 +30,38 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages
         private IObjectModelValidator _objectValidator;
         private ITempDataDictionary _tempData;
         private IUrlHelper _urlHelper;
+        private PageContext _pageContext;
 
         /// <summary>
         /// Gets the <see cref="RazorPages.PageContext"/>.
         /// </summary>
         [PageContext]
-        public PageContext PageContext { get; set; }
+        public PageContext PageContext
+        {
+            get
+            {
+                if (_pageContext == null)
+                {
+                    _pageContext = new PageContext();
+                }
+
+                return _pageContext;
+            }
+            set
+            {
+                if (value == null)
+                {
+                    throw new ArgumentNullException(nameof(value));
+                }
+
+                _pageContext = value;
+            }
+        }
 
         /// <summary>
         /// Gets the <see cref="Http.HttpContext"/>.
         /// </summary>
-        public HttpContext HttpContext => PageContext?.HttpContext;
+        public HttpContext HttpContext => PageContext.HttpContext;
 
         /// <summary>
         /// Gets the <see cref="HttpRequest"/>.

test/Microsoft.AspNetCore.Mvc.RazorPages.Test/PageModelTest.cs

@@ -24,6 +24,16 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages
 {
     public class PageModelTest
     {
+        [Fact]
+        public void PageContext_GetsInitialized()
+        {
+            // Arrange
+            var pageModel = new TestPageModel();
+
+            // Act & Assert
+            Assert.NotNull(pageModel.PageContext);
+        }
+
         [Fact]
         public void Redirect_WithParameterUrl_SetsRedirectResultSameUrl()
         {