Don't pass host_web_client flag to register_servlets, it needs to be a Resource not a RestServlet.

synapse/app/homeserver.py

@@ -148,7 +148,7 @@ def setup():
     # the replication layer
     hs.get_federation()
 
-    hs.register_servlets(host_web_client=args.webclient)
+    hs.register_servlets()
 
     hs.get_http_server().start_listening(args.port)
 

synapse/server.py

@@ -171,7 +171,7 @@ class HomeServer(BaseHomeServer):
     def build_distributor(self):
         return Distributor()
 
-    def register_servlets(self, host_web_client):
+    def register_servlets(self):
         """ Register all servlets associated with this HomeServer.
 
         Args:
@@ -179,5 +179,3 @@ class HomeServer(BaseHomeServer):
         """
         # Simply building the ServletFactory is sufficient to have it register
         factory = self.get_rest_servlet_factory()
-        if host_web_client:
-            factory.register_web_client(self)