Filter 为什么从数组中筛选未定义的值不起作用？

这是我的代码：

.subscribe(data => {
  const openTickets = data.map(d => d.tickets.map(t => {
    if (t.customerStatus !== 'closed'){
      return {serialNumber: d.serialNumber.trim(), id: t.id} ;
    }
  }));
  // openTickets = [undefined, {serialNumber: 9082347, id: 59}]
  this.ticketsOpen = openTickets.filter(t => t !== undefined);
  console.log(this.ticketsOpen)
  this.ticketsOpen = [undefined, {serialNumber: 9082347, id: 59}]
})

我不明白为什么过滤方法不起作用。我也试过了

openTickets.filter(t => !!t);