Using set instead of add in Created ActionResults

src/Microsoft.AspNet.Mvc.Core/ActionResults/CreatedAtActionResult.cs

@@ -71,7 +71,7 @@ namespace Microsoft.AspNet.Mvc
                 throw new InvalidOperationException(Resources.NoRoutesMatched);
             }
 
-            context.HttpContext.Response.Headers.Add("Location", new string[] { url });
+            context.HttpContext.Response.Headers.Set("Location", url);
         }
     }
 }

src/Microsoft.AspNet.Mvc.Core/ActionResults/CreatedAtRouteResult.cs

@@ -69,7 +69,7 @@ namespace Microsoft.AspNet.Mvc
                 throw new InvalidOperationException(Resources.NoRoutesMatched);
             }
 
-            context.HttpContext.Response.Headers.Add("Location", new string[] { url });
+            context.HttpContext.Response.Headers.Set("Location", url);
         }
     }
 }

src/Microsoft.AspNet.Mvc.Core/ActionResults/CreatedResult.cs

@@ -31,7 +31,7 @@ namespace Microsoft.AspNet.Mvc
         /// <inheritdoc />
         protected override void OnFormatting([NotNull] ActionContext context)
         {
-            context.HttpContext.Response.Headers.Add("Location", new string[] { Location });
+            context.HttpContext.Response.Headers.Set("Location", Location);
         }
     }
 }

test/Microsoft.AspNet.Mvc.Core.Test/ActionResults/CreatedResultTests.cs

@@ -45,6 +45,24 @@ namespace Microsoft.AspNet.Mvc
             Assert.Equal(location, httpContext.Response.Headers["Location"]);
         }
 
+        [Fact]
+        public async Task CreatedResult_OverwritesLocationHeader()
+        {
+            // Arrange
+            var location = "/test/";
+            var httpContext = GetHttpContext();
+            var actionContext = GetActionContext(httpContext);
+            httpContext.Response.Headers.Set("Location", "/different/location/");
+            var result = new CreatedResult(location, "testInput");
+
+            // Act
+            await result.ExecuteResultAsync(actionContext);
+
+            // Assert
+            Assert.Equal(201, httpContext.Response.StatusCode);
+            Assert.Equal(location, httpContext.Response.Headers["Location"]);
+        }
+
         private static ActionContext GetActionContext(HttpContext httpContext)
         {
             var routeData = new RouteData();