Added a method to check if the server is running

NodeLookupReceiver
Only use the server if it's running

src/kademlia/core/KadServer.java

@@ -221,7 +221,7 @@ public class KadServer
                         }
                         catch (InterruptedException ex)
                         {
-                            
+
                         }
                     }
 
@@ -349,4 +349,9 @@ public class KadServer
         }
     }
 
+    public boolean isRunning()
+    {
+        return this.isRunning;
+    }
+
 }

src/kademlia/message/NodeLookupReceiver.java

@@ -51,8 +51,11 @@ public class NodeLookupReceiver implements Receiver
         /* Respond to the NodeLookupMessage */
         Message reply = new NodeReplyMessage(this.localNode.getNode(), nodes);
 
-        /* Let the Server send the reply */
-        this.server.reply(origin, reply, comm);
+        if (this.server.isRunning())
+        {
+            /* Let the Server send the reply */
+            this.server.reply(origin, reply, comm);
+        }
     }
 
     /**