Python-owasp-zap api

Question

I want to use python-owasp-zap api. I downloaded and installed all the repositories required for python-owasp-zap. When I run the sample code which was given in the web site https://code.google.com/p/zaproxy/wiki/ApiPython I get the following error, please help me.

zap.spider.scan(target)
 return self.zap._request(self.zap.base + 'spider/action/scan/',                        {'url' : url, 'apikey' : apikey})

 File "/usr/local/lib/python2.7/dist-packages/zapv2/spider.py", line 108, in scan
 return json.loads(self.urlopen(url + '?' + urllib.urlencode(get)))
 File "/usr/lib/python2.7/json/decoder.py", line 366, in decode
obj, end = self.raw_decode(s, idx=_w(s, 0).end())
File "/usr/lib/python2.7/json/decoder.py", line 384, in raw_decode
raise ValueError("No JSON object could be decoded")
ValueError: No JSON object could be decoded