Throw PtcOfflineException on maintenance

diff --git a/PokemonGo.RocketAPI/Login/PtcLogin.cs b/PokemonGo.RocketAPI/Login/PtcLogin.cs
index aa6e94c..19f5078 100644
--- a/PokemonGo.RocketAPI/Login/PtcLogin.cs
+++ b/PokemonGo.RocketAPI/Login/PtcLogin.cs
@@ -16,7 +16,7 @@ namespace PokemonGo.RocketAPI.Login
     {
         public static async Task<string> GetAccessToken(string username, string password)
         {
-            var handler = new HttpClientHandler()
+            var handler = new HttpClientHandler
             {
                 AutomaticDecompression = DecompressionMethods.GZip,
                 AllowAutoRedirect = false
@@ -27,6 +27,11 @@ namespace PokemonGo.RocketAPI.Login
                 //Get session cookie
                 var sessionResp = await tempHttpClient.GetAsync(Resources.PtcLoginUrl);
                 var data = await sessionResp.Content.ReadAsStringAsync();
+                if (data == null) throw new PtcOfflineException();
+
+                if (sessionResp.StatusCode == HttpStatusCode.InternalServerError || data.Contains("<title>Maintenance"))
+                    throw new PtcOfflineException();
+
                 var lt = JsonHelper.GetValue(data, "lt");
                 var executionId = JsonHelper.GetValue(data, "execution");

@@ -39,7 +44,7 @@ namespace PokemonGo.RocketAPI.Login
                             new KeyValuePair<string, string>("execution", executionId),
                             new KeyValuePair<string, string>("_eventId", "submit"),
                             new KeyValuePair<string, string>("username", username),
-                            new KeyValuePair<string, string>("password", password),
+                            new KeyValuePair<string, string>("password", password)
                         }));

                 if (loginResp.Headers.Location == null)
@@ -60,7 +65,7 @@ namespace PokemonGo.RocketAPI.Login
                             new KeyValuePair<string, string>("client_secret",
                                 "w8ScCUXJQc6kXKw8FiOhd8Fixzht18Dq3PEVkUCP5ZPxtgyWsbTvWHFLm2wNY0JR"),
                             new KeyValuePair<string, string>("grant_type", "refresh_token"),
-                            new KeyValuePair<string, string>("code", ticketId),
+                            new KeyValuePair<string, string>("code", ticketId)
                         }));

                 var tokenData = await tokenResp.Content.ReadAsStringAsync();
@@ -68,4 +73,4 @@ namespace PokemonGo.RocketAPI.Login
             }
         }
     }
-}
+}
\ No newline at end of file