From fcc27fd4e27b407cfdf86e8a8b6ce00ba361af57 Mon Sep 17 00:00:00 2001
From: sta <sta.blockhead@gmail.com>
Date: Wed, 16 Aug 2017 11:46:12 +0900
Subject: [PATCH] [Modify] Throw exception

---
 websocket-sharp/Server/WebSocketSessionManager.cs | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/websocket-sharp/Server/WebSocketSessionManager.cs b/websocket-sharp/Server/WebSocketSessionManager.cs
index 6e7cde7d..fac22909 100644
--- a/websocket-sharp/Server/WebSocketSessionManager.cs
+++ b/websocket-sharp/Server/WebSocketSessionManager.cs
@@ -1216,11 +1216,17 @@ namespace WebSocketSharp.Server
     /// the send is complete. A <see cref="bool"/> passed to this delegate is <c>true</c>
     /// if the send is complete successfully.
     /// </param>
-    public void SendToAsync (Stream stream, int length, string id, Action<bool> completed)
+    public void SendToAsync (
+      Stream stream, int length, string id, Action<bool> completed
+    )
     {
       IWebSocketSession session;
-      if (TryGetSession (id, out session))
-        session.Context.WebSocket.SendAsync (stream, length, completed);
+      if (!TryGetSession (id, out session)) {
+        var msg = "The session could not be found.";
+        throw new ArgumentException (msg, "id");
+      }
+
+      session.Context.WebSocket.SendAsync (stream, length, completed);
     }
 
     /// <summary>