def METHOD_NAME(self, url, json=None):
    if not self.server:
        return None
    try:
        res = requests.post(self.server + '/' + url, json=json,
                            timeout=self.TIMEOUT)
        return res.json()
    except requests.exceptions.RequestException as e:
        if callable(self.on_server_down):
            self.on_server_down(str(e))
        return None