title: How to solve error with bottlenose getting an empty object: expected string or bytes-like object
body: <p>I'm running my code on a server, and the connection to Amazon works correct when I first boot at the server, but after some requests it fails all the time. If I restart the server it starts working again, but then fails on the same previous situation. I've tried changing the IP from the server, to check if my IP was blocked. But that wasn't the case. I'm not getting a clear error from the API, only an empty object error, so I can't figure out how to solve the issue.</p>
  
  <p>Here is the error:</p>
  
  <pre><code>Traceback (most recent call last):
    File "/usr/local/lib/python3.5/dist-packages/amazon/api.py", line 174, in lookup
      response = self.api.ItemLookup(ResponseGroup=ResponseGroup, **kwargs)
    File "/usr/local/lib/python3.5/dist-packages/bottlenose/api.py", line 274, in __call__
      {'api_url': api_url, 'cache_url': cache_url})
    File "/usr/local/lib/python3.5/dist-packages/bottlenose/api.py", line 235, in _call_api
      return urllib2.urlopen(api_request, timeout=self.Timeout)
    File "/usr/lib/python3.5/urllib/request.py", line 163, in urlopen
      return opener.open(url, data, timeout)
    File "/usr/lib/python3.5/urllib/request.py", line 466, in open
      response = self._open(req, data)
    File "/usr/lib/python3.5/urllib/request.py", line 484, in _open
      '_open', req)
    File "/usr/lib/python3.5/urllib/request.py", line 444, in _call_chain
      result = func(*args)
    File "/usr/lib/python3.5/urllib/request.py", line 1297, in https_open
      context=self._context, check_hostname=self._check_hostname)
    File "/usr/lib/python3.5/urllib/request.py", line 1254, in do_open
      h.request(req.get_method(), req.selector, req.data, headers)
    File "/usr/lib/python3.5/http/client.py", line 1107, in request
      self._send_request(method, url, body, headers)
    File "/usr/lib/python3.5/http/client.py", line 1147, in _send_request
      self.putheader(hdr, value)
    File "/usr/lib/python3.5/http/client.py", line 1083, in putheader
      if _is_illegal_header_value(values[i]):
  TypeError: expected string or bytes-like object
  </code></pre>
  
  <p>Thanks a lot!</p>