Exception running PyHawk client using requests 2.2.1

gistfile1.py

> /home/gavin/dev/gavin/hawkeye/useful/pyhawk/mycode/sample_client.py(53)<module>()->None
-> main()
(Pdb) c
Traceback (most recent call last):
  File "sample_client.py", line 53, in <module>
    main()
  File "sample_client.py", line 33, in main
    res = requests.get(url, data=params, headers=headers)
  File "/home/gavin/dev/gavin/hawkeye/useful/pyhawk/local/lib/python2.7/site-packages/requests/api.py", line 55, in get
    return request('get', url, **kwargs)
  File "/home/gavin/dev/gavin/hawkeye/useful/pyhawk/local/lib/python2.7/site-packages/requests/api.py", line 44, in request
    return session.request(method=method, url=url, **kwargs)
  File "/home/gavin/dev/gavin/hawkeye/useful/pyhawk/local/lib/python2.7/site-packages/requests/sessions.py", line 349, in request
    prep = self.prepare_request(req)
  File "/home/gavin/dev/gavin/hawkeye/useful/pyhawk/local/lib/python2.7/site-packages/requests/sessions.py", line 287, in prepare_request
    hooks=merge_hooks(request.hooks, self.hooks),
  File "/home/gavin/dev/gavin/hawkeye/useful/pyhawk/local/lib/python2.7/site-packages/requests/models.py", line 288, in prepare
    self.prepare_headers(headers)
  File "/home/gavin/dev/gavin/hawkeye/useful/pyhawk/local/lib/python2.7/site-packages/requests/models.py", line 387, in prepare_headers
    self.headers = CaseInsensitiveDict((to_native_string(name), value) for name, value in headers.items())
AttributeError: 'list' object has no attribute 'items'