目前项目有很多未定义的崩溃

class Data { 
  order_id: number | undefined = 0 
  pay_tips: string | undefined = '' 
  pay_deadline: string | undefined = '' 
  time: string | undefined = '' 
}
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//崩溃 -- b.data.pay_deadline 会提示有可能为undefined 
 
if (b.data.pay_deadline.length) { 
  console.info("b.data.pay_deadline is not null") 
} 
//崩溃 -- b.data.time 会提示有可能为undefined 
if (b.data.time.length > 0) { 
  console.info("b.data.time is not null") 
}
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