message: fixed crash error for ttl
diff: @@ -99,7 +99,10 @@ bool CommonUtils::checkDataExpiredForTTL(const meta::SchemaProviderIf* schema,
  }
  auto now = time::WallClock::fastNowInSec();
  auto v = reader->getValueByName(ttlCol);
  - if (now > (v.getInt() + ttlDuration)) {
  +
  + // if the value is not INT type (sush as NULL), it will never expire.
  + // TODO (sky) : DateTime
  + if (v.isInt() && (now > (v.getInt() + ttlDuration))) {
  VLOG(2) << "ttl expired";
  return true;
  }
  