Address comments

Emby.Server.Implementations/Services/ServiceExec.cs

@@ -111,7 +111,8 @@ namespace Emby.Server.Implementations.Services
                     CultureInfo.InvariantCulture,
                     "Could not find method named {1}({0}) or Any({0}) on Service {2}",
                     requestDto.GetType().GetMethodName(),
-                    expectedMethodName, serviceType.GetMethodName()));
+                    expectedMethodName,
+                    serviceType.GetMethodName()));
         }
 
         private static async Task<object> GetTaskResult(Task task)

Emby.Server.Implementations/Services/ServiceHandler.cs

@@ -2,6 +2,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Net.Mime;
 using System.Reflection;
 using System.Threading;
 using System.Threading.Tasks;
@@ -59,11 +60,11 @@ namespace Emby.Server.Implementations.Services
         {
             if (format.Equals("json", StringComparison.Ordinal))
             {
-                return "application/json";
+                return MediaTypeNames.Application.Json;
             }
             else if (format.Equals("xml", StringComparison.Ordinal))
             {
-                return "application/xml";
+                return MediaTypeNames.Application.Xml;
             }
 
             return null;