protected function assertPayload($aPayload = null)
    {
        if (! array_key_exists('enabled', $aPayload) || ! array_key_exists('interval', $aPayload)) {
            throw new \InvalidArgumentException('Payload does not contain a enabled or interval key');
        }

        if (! is_bool($aPayload['enabled'])) throw new \InvalidArgumentException('Enabled flag must be a boolean value');
        if (! is_int($aPayload['interval'])) throw new \InvalidArgumentException('Ticker interval must be an integer');
    }