Adding end-to-end test

src/Mvc/test/Mvc.FunctionalTests/NonNullableReferenceTypesTest.cs

@@ -1,4 +1,4 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
@@ -106,4 +106,18 @@ public async Task CanUseNonNullableReferenceType_WithController_SubmitData_NoErr
         // Redirect means there were no validation errors.
         await response.AssertStatusCodeAsync(HttpStatusCode.Redirect);
     }
+
+    [Fact]
+    public async Task CanUseNonNullableReferenceType_WithController_DefaultValueParameter_NoError()
+    {
+        // Act 1
+        var response = await Client.GetAsync("http://localhost/api/NonNullable");
+
+        // Assert 1
+        _ = await response.AssertStatusCodeAsync(HttpStatusCode.OK);
+        var content = await response.Content.ReadAsStringAsync();
+
+        // Assert 2
+        Assert.NotNull(content);
+    }
 }

src/Mvc/test/WebSites/BasicWebSite/Controllers/NonNullableApiController.cs

@@ -0,0 +1,23 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#nullable enable
+using Microsoft.AspNetCore.Mvc;
+
+namespace BasicWebSite.Controllers;
+
+#nullable enable
+
+[ApiController]
+[Route("api/NonNullable")]
+public class NonNullableApiController : ControllerBase
+{
+    // GET: api/<controller>
+    [HttpGet]
+    public ActionResult<string> Get(string language = "pt-br")
+    {
+        return language;
+    }
+}
+
+#nullable restore