我试图获取文档数组的第一个元素。如您所见，“primera”字段在结果中为空:{"_id":ObjectId("5bb164d71d2eef353d292cab"),"asunto":{"id":"5b48bb7251b997b3cc23b9e4","abreviatura":"AF","titulo":"AlarmaFuente","descripcion":"Alarmageneradaporuneventodeenergíaenlafuente."},"tiempos":[{"cola":"5b55f8a351b9979f1e417b43","inicio":1538352343