'Get the issue specified by ``number``.
:param int number: (required), number of the issue on this repository
:returns: :class:`Issue <github3.issues.issue.Issue>` if successful,
otherwise None'

def issue(self, number):

    json = None
    if (int(number) > 0):
        url = self._build_url(u'issues', str(number), base_url=self._api)
        json = self._json(self._get(url), 200)
    return self._instance_or_null(Issue, json)
