假設值firsName和lastName來自某些數據源。該值有時可能為null或都未定義。fullName將兩者結合在一起。let a = {};let b = {    fullName: a && a.firstName+' '+a.lastName};console.log("fullName is "+JSON.stringify(b.fullName)); // fullName is "undefined undefined"a = {    firstName: null,    lastName: null};b = {    fullName: a.firstName+' '+a.lastName};console.log("fullName is "+JSON.stringify(b.fullName)); // fullName is "null null"b = {    fullName: {...a.firstName, ...' ', ...a.lastName}};console.log("fullName is "+JSON.stringify(b.fullName)); // fullName is {"0":" "}b = {    fullName: {...a.firstName, ...a.lastName}};console.log("fullName is "+JSON.stringify(b.fullName)); // fullName is {}我當前的解決方案是const getFullName = (firstName, lastName ) => {    if ((typeof firstName == "undefined" || firstName === null) && (typeof lastName == "undefined" || lastName === null)) {            return null;    }    else {         return firstName+' '+lastName    }}b = {    fullName: getFullName(a.firstName, a.lastName)};console.log("fullName with function is "+JSON.stringify(b.fullName)); // fullName with function is nulla = {};console.log("fullName with function is "+JSON.stringify(b.fullName)); // fullName with function is null有沒有更好的方法來使b.fullName的值為null（無需編寫函數）？