Fix broken query string binding test

This test was relying on the parsing behavior of QueryString, that it
would omit the key and value when the value is empty. The expectations
weren't consistent with other tests for 'empty' values.

test/Microsoft.AspNetCore.Mvc.IntegrationTests/MutableObjectModelBinderIntegrationTest.cs

@@ -10,6 +10,7 @@ using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Http.Internal;
 using Microsoft.AspNetCore.Mvc.Abstractions;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
+using Microsoft.AspNetCore.Testing;
 using Microsoft.Extensions.Primitives;
 using Xunit;
 
@@ -1887,10 +1888,11 @@ namespace Microsoft.AspNetCore.Mvc.IntegrationTests
             Assert.Null(error.Exception);
         }
 
-        // This covers the case where a key is present, but has no value. The type converter
-        // will report an error.
+        // This covers the case where a key is present, but has no value. The model binder will
+        // report and error because it's a value type (non-nullable).
         [Fact]
-        public async Task MutableObjectModelBinder_BindsPOCO_TypeConvertedPropertyWithNoValue_NoError()
+        [ReplaceCulture]
+        public async Task MutableObjectModelBinder_BindsPOCO_TypeConvertedPropertyWithEmptyValue_Error()
         {
             // Arrange
             var argumentBinder = ModelBindingTestHelper.GetArgumentBinder();
@@ -1918,9 +1920,16 @@ namespace Microsoft.AspNetCore.Mvc.IntegrationTests
             Assert.NotNull(model);
             Assert.Equal(0, model.ProductId);
 
-            Assert.Equal(0, modelState.Count);
-            Assert.Equal(0, modelState.ErrorCount);
-            Assert.True(modelState.IsValid);
+            var entry = Assert.Single(modelState);
+            Assert.Equal("parameter.ProductId", entry.Key);
+            Assert.Equal(string.Empty, entry.Value.AttemptedValue);
+
+            var error = Assert.Single(entry.Value.Errors);
+            Assert.Equal("The value '' is invalid.", error.ErrorMessage, StringComparer.Ordinal);
+            Assert.Null(error.Exception);
+
+            Assert.Equal(1, modelState.ErrorCount);
+            Assert.False(modelState.IsValid);
         }
 
         private static void SetJsonBodyContent(HttpRequest request, string content)