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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def assign_issue(self, issue, assignee):
 """Assign an issue to a user. None will set it to unassigned. -1 will set it to Automatic. :param issue: the issue ID or key to assign :type issue: int or str :param assignee: the user to assign the issue to :type assignee: str :rtype: bool """

        url = self._options['server'] + \
            '/rest/api/latest/issue/' + str(issue) + '/assignee'
        payload = {'name': assignee}
        r = self._session.put(
            url, data=json.dumps(payload))
        raise_on_error(r)
        return True