add error catch

main.py

@@ -45,6 +45,14 @@ async def on_message(message):
 
     if message.content.startswith(BOTDATA['prefix'] + 'hello'):
         await message.channel.send("Hello, {}!".format(message.author))
-      
+
+@client.event
+async def on_error(event, *args, **kwargs):
+    with open('err.log', 'a') as f:
+        if event == 'on_message':
+            f.write(f'Unhandled message: {args[0]}\n')
+        else:
+            raise
+
 #keep_alive()
 client.run(BOTDATA['token'])