From 4625266db6047b78c91d1a97f63738955adb237b Mon Sep 17 00:00:00 2001
From: AlexejStukov <sergej.morokin@googlemail.com>
Date: Fri, 22 Jul 2016 08:17:49 +0200
Subject: [PATCH] raise error if self.fields is empty

---
 channels/binding/websockets.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/channels/binding/websockets.py b/channels/binding/websockets.py
index b211442..fcd97ef 100644
--- a/channels/binding/websockets.py
+++ b/channels/binding/websockets.py
@@ -56,6 +56,8 @@ class WebsocketBinding(Binding):
         """
         if self.fields == ['__all__']:
             self.fields = None
+        elif not self.fields:
+            raise ValueError("You must set the fields attribute on Binding %r!" % self.__class__)
         data = serializers.serialize('json', [instance], fields=self.fields)
         return json.loads(data)[0]['fields']