fixup! Don't fall back to Apollo when not in subprotocols

Author: jaylett

gql/transport/websockets_protocol.py

@@ -483,7 +483,7 @@ async def _after_connect(self):
         except KeyError:
             # If the server does not send the subprotocol header, use
             # the apollo subprotocol by default unless we didn't ask for it
-            if self.APOLLO_SUBPROTOCOL in self.adapter.subprotocols:
+            if self.adapter.subprotocols is None or self.APOLLO_SUBPROTOCOL in self.adapter.subprotocols:
                 self.subprotocol = self.APOLLO_SUBPROTOCOL
             else:
                 self.subprotocol = self.GRAPHQLWS_SUBPROTOCOL