Fixing compilation error.

Hi, 
    Thanks for pulling this. There is a small compilation error.
I will keep working on this to make it better.
LGTM for the api change you did regarding WriteResponse.
JSON RPC 2 send errors as 200 OK, with error set in the response object.
If anything fishy happens during write response, I set 400. Let me know if you wanna change it.

Regards,
Ranveer.