node.js异常对象在try / catch块中为空

Question

在以下功能中：

cmd.exe

我收到以下日志消息：

function processDeviceOffline(deviceID) {
  var sqlstr = sql.format("SELECT Location, Name FROM devices WHERE DeviceID = ?", [deviceID]);
  var query = db.query(sqlstr, function(err, result){
    try {
        if (err) {
          console.log("processDeviceOffline SQL error: %j", err);
          console.log('When '+deviceID+' reported Offline');
        } else {
          if (result[0]) {
            utils.notify('Device Offline: '+result[0].Name+'-'+result[0].Location+')');
          } else {
            utils.notify(`Unknown Device Offline: ${deviceID}`);
          }
        }
    } catch(ex) {
      console.log("processDeviceOffline %j (%j)", ex, result);
    }
  });
}

为什么异常对象'ex'为空？