Check and update the object with conditional request
        :rtype: Boolean value indicating whether the object is changed

def update(self):
        '''
        Check and update the object with conditional request
        :rtype: Boolean value indicating whether the object is changed
        '''
        conditionalRequestHeader = dict()
        if self.etag is not None:
            conditionalRequestHeader[Consts.REQ_IF_NONE_MATCH] = self.etag
        if self.last_modified is not None:
            conditionalRequestHeader[Consts.REQ_IF_MODIFIED_SINCE] = self.last_modified

        status, responseHeaders, output = self._requester.requestJson(
            "GET",
            self._url.value,
            headers=conditionalRequestHeader
        )
        if status == 304:
            return False
        else:
            headers, data = self._requester._Requester__check(status, responseHeaders, output)
            self._storeAndUseAttributes(headers, data)
            self.__completed = True
            return True