Do not return ProblemDetails for < 4xx status codes

Fixes #8504

src/Microsoft.AspNetCore.Mvc.Core/Infrastructure/ClientErrorResultFilter.cs

@@ -43,6 +43,13 @@ namespace Microsoft.AspNetCore.Mvc.Infrastructure
                 return;
             }
 
+            // We do not have an upper bound on the allowed status code. This allows this filter to be used
+            // for 5xx and later status codes.
+            if (clientError.StatusCode < 400)
+            {
+                return;
+            }
+
             var result = _clientErrorFactory.GetClientError(context, clientError);
             if (result == null)
             {

test/Microsoft.AspNetCore.Mvc.Core.Test/Infrastructure/ClientErrorResultFilterTest.cs

@@ -68,6 +68,42 @@ namespace Microsoft.AspNetCore.Mvc.Infrastructure
             Assert.Same(Result, context.Result);
         }
 
+        [Theory]
+        [InlineData(400)]
+        [InlineData(409)]
+        [InlineData(503)]
+        public void OnResultExecuting_Transforms4XXStatusCodeResult(int statusCode)
+        {
+            // Arrange
+            var actionResult = new StatusCodeResult(statusCode);
+            var context = GetContext(actionResult);
+            var filter = GetFilter();
+
+            // Act
+            filter.OnResultExecuting(context);
+
+            // Assert
+            Assert.Same(Result, context.Result);
+        }
+
+        [Theory]
+        [InlineData(201)]
+        [InlineData(302)]
+        [InlineData(399)]
+        public void OnResultExecuting_DoesNotTransformStatusCodesLessThan400(int statusCode)
+        {
+            // Arrange
+            var actionResult = new StatusCodeResult(statusCode);
+            var context = GetContext(actionResult);
+            var filter = GetFilter();
+
+            // Act
+            filter.OnResultExecuting(context);
+
+            // Assert
+            Assert.Same(actionResult, context.Result);
+        }
+
         private static ClientErrorResultFilter GetFilter()
         {
             var factory = Mock.Of<IClientErrorFactory>(