[Blazor] Allow null parameter values to be supplied to interactive components via enhanced page update

src/Components/Endpoints/test/WebRootComponentParametersTest.cs

@@ -100,36 +100,73 @@ public void WebRootComponentParameters_DefinitelyEquals_ReturnsTrue_ForEmptySetO
     }
 
     [Fact]
-    public void WebRootComponentParameters_DefinitelyEquals_Throws_WhenComparingNonJsonElementParameterToJsonElement()
+    public void WebRootComponentParameters_DefinitelyEquals_ReturnsFalse_WhenComparingNonJsonElementParameterToJsonElement()
     {
         // Arrange
         var parameters1 = CreateParametersWithNonJsonElements(new() { ["First"] = 123 });
         var parameters2 = CreateParameters(new() { ["First"] = 456 });
 
-        // Act/assert
-        Assert.Throws<InvalidCastException>(() => parameters1.DefinitelyEquals(parameters2));
+        // Act
+        var result = parameters1.DefinitelyEquals(parameters2);
+
+        // Assert
+        Assert.False(result);
     }
 
     [Fact]
-    public void WebRootComponentParameters_DefinitelyEquals_Throws_WhenComparingJsonElementParameterToNonJsonElement()
+    public void WebRootComponentParameters_DefinitelyEquals_ReturnsFalse_WhenComparingJsonElementParameterToNonJsonElement()
     {
         // Arrange
         var parameters1 = CreateParameters(new() { ["First"] = 123 });
         var parameters2 = CreateParametersWithNonJsonElements(new() { ["First"] = 456 });
 
-        // Act/assert
-        Assert.Throws<InvalidCastException>(() => parameters1.DefinitelyEquals(parameters2));
+        // Act
+        var result = parameters1.DefinitelyEquals(parameters2);
+
+        // Assert
+        Assert.False(result);
+    }
+
+    [Fact]
+    public void WebRootComponentParameters_DefinitelyEquals_ReturnsTrue_WhenComparingEqualNonJsonElementParameters()
+    {
+        // Arrange
+        var parameters1 = CreateParametersWithNonJsonElements(new() { ["First"] = 123 });
+        var parameters2 = CreateParametersWithNonJsonElements(new() { ["First"] = 123 });
+
+        // Act
+        var result = parameters1.DefinitelyEquals(parameters2);
+
+        // Assert
+        Assert.True(result);
     }
 
     [Fact]
-    public void WebRootComponentParameters_DefinitelyEquals_Throws_WhenComparingNonJsonElementParameters()
+    public void WebRootComponentParameters_DefinitelyEquals_ReturnsFalse_WhenComparingInequalNonJsonElementParameters()
     {
         // Arrange
         var parameters1 = CreateParametersWithNonJsonElements(new() { ["First"] = 123 });
         var parameters2 = CreateParametersWithNonJsonElements(new() { ["First"] = 456 });
 
-        // Act/assert
-        Assert.Throws<InvalidCastException>(() => parameters1.DefinitelyEquals(parameters2));
+        // Act
+        var result = parameters1.DefinitelyEquals(parameters2);
+
+        // Assert
+        Assert.False(result);
+    }
+
+    [Fact]
+    public void WebRootComponentParameters_DefinitelyEquals_ReturnsTrue_WhenComparingNullParameters()
+    {
+        // Arrange
+        var parameters1 = CreateParametersWithNonJsonElements(new() { ["First"] = null });
+        var parameters2 = CreateParametersWithNonJsonElements(new() { ["First"] = null });
+
+        // Act
+        var result = parameters1.DefinitelyEquals(parameters2);
+
+        // Assert
+        Assert.True(result);
     }
 
     private static WebRootComponentParameters CreateParameters(Dictionary<string, object> parameters)

src/Components/Shared/src/WebRootComponentParameters.cs

@@ -45,9 +45,17 @@ public bool DefinitelyEquals(in WebRootComponentParameters other)
                 return false;
             }
 
-            var value = ((JsonElement)_serializedParameterValues[i]).GetRawText();
-            var otherValue = ((JsonElement)other._serializedParameterValues[i]).GetRawText();
-            if (!string.Equals(value, otherValue, StringComparison.Ordinal))
+            // We expect each serialized parameter value to be either a 'JsonElement' or 'null'.
+            var value = _serializedParameterValues[i];
+            var otherValue = other._serializedParameterValues[i];
+            if (value is JsonElement jsonValue && otherValue is JsonElement otherJsonValue)
+            {
+                if (!string.Equals(jsonValue.GetRawText(), otherJsonValue.GetRawText(), StringComparison.Ordinal))
+                {
+                    return false;
+                }
+            }
+            else if (!Equals(value, otherValue))
             {
                 return false;
             }

src/Components/test/E2ETest/ServerRenderingTests/EnhancedNavigationTest.cs

@@ -597,6 +597,36 @@ public void LocationChangingEventGetsInvokedOnEnhancedNavigationOnlyForRuntimeTh
         Browser.Equal("0", () => Browser.Exists(By.Id($"location-changing-count-{anotherRuntime}")).Text);
     }
 
+    [Theory]
+    [InlineData("server")]
+    [InlineData("wasm")]
+    public void CanReceiveNullParameterValueOnEnhancedNavigation(string renderMode)
+    {
+        // See: https://github.com/dotnet/aspnetcore/issues/52434 
+        Navigate($"{ServerPathBase}/nav");
+        Browser.Equal("Hello", () => Browser.Exists(By.TagName("h1")).Text);
+
+        Browser.Exists(By.TagName("nav")).FindElement(By.LinkText($"Null component parameter ({renderMode})")).Click();
+        Browser.Equal("Page rendering component with null parameter", () => Browser.Exists(By.TagName("h1")).Text);
+        Browser.Equal("0", () => Browser.Exists(By.Id("current-count")).Text);
+
+        Browser.Exists(By.Id("button-increment")).Click();
+        Browser.Equal("1", () => Browser.Exists(By.Id("current-count")).Text);
+
+        // This refresh causes the interactive component to receive a 'null' parameter value
+        Browser.Exists(By.Id("button-refresh")).Click();
+        Browser.Equal("1", () => Browser.Exists(By.Id("current-count")).Text);
+
+        // Increment the count again to ensure that interactivity still works
+        Browser.Exists(By.Id("button-increment")).Click();
+        Browser.Equal("2", () => Browser.Exists(By.Id("current-count")).Text);
+
+        // Even if the interactive runtime continues to function (as the WebAssembly runtime might),
+        // fail the test if any errors were logged to the browser console
+        var logs = Browser.GetBrowserLogs(LogLevel.Warning);
+        Assert.DoesNotContain(logs, log => log.Message.Contains("Error"));
+    }
+
     private void AssertEnhancedUpdateCountEquals(long count)
         => Browser.Equal(count, () => ((IJavaScriptExecutor)Browser).ExecuteScript("return window.enhancedPageUpdateCount;"));
 

src/Components/test/testassets/Components.TestServer/RazorComponents/Pages/EnhancedNav/PageRenderingComponentWithNullParameter.razor

@@ -0,0 +1,24 @@
+@page "/nav/null-parameter/{mode}"
+@using TestContentPackage
+
+@* https://github.com/dotnet/aspnetcore/issues/52434 *@
+
+<h1>Page rendering component with null parameter</h1>
+
+@if (Mode == "server")
+{
+    <ComponentAcceptingNullParameter @rendermode="RenderMode.InteractiveServer" Value="@null" />
+}
+else if (Mode == "wasm")
+{
+    <ComponentAcceptingNullParameter @rendermode="RenderMode.InteractiveWebAssembly" Value="@null" />
+}
+else
+{
+    <p>Expected a render mode of 'server' or 'wasm', but got '@Mode'.</p>
+}
+
+@code {
+    [Parameter]
+    public string? Mode { get; set; }
+}

src/Components/test/testassets/Components.TestServer/RazorComponents/Shared/EnhancedNavLayout.razor

@@ -23,6 +23,8 @@
     <NavLink href="nav/location-changed/server">LocationChanged/LocationChanging event (server)</NavLink>
     <NavLink href="nav/location-changed/wasm">LocationChanged/LocationChanging event (wasm)</NavLink>
     <NavLink href="nav/location-changed/server-and-wasm">LocationChanged/LocationChanging event (server-and-wasm)</NavLink>
+    <NavLink href="nav/null-parameter/server">Null component parameter (server)</NavLink>
+    <NavLink href="nav/null-parameter/wasm">Null component parameter (wasm)</NavLink>
     <br />
     <a href="nav/other" data-enhance-nav="false">
         <svg width="100" height="100" id="svg-in-anchor-not-enhanced-nav-link">

src/Components/test/testassets/TestContentPackage/ComponentAcceptingNullParameter.razor

@@ -0,0 +1,36 @@
+@inject NavigationManager NavigationManager
+
+<p>Value: @(Value ?? "(null)")</p>
+
+@if (_interactive)
+{
+    <button id="button-increment" @onclick="Increment">Count: <span id="current-count">@_count</span></button>
+    <button id="button-refresh" @onclick="Refresh">Refresh</button>
+}
+
+@code {
+    private bool _interactive;
+    private int _count;
+
+    [Parameter]
+    public string Value { get; set; }
+
+    protected override void OnAfterRender(bool firstRender)
+    {
+        if (firstRender)
+        {
+            _interactive = true;
+            StateHasChanged();
+        }
+    }
+
+    private void Increment()
+    {
+        _count++;
+    }
+
+    private void Refresh()
+    {
+        NavigationManager.Refresh();
+    }
+}