如何在 Angular 中处理空值

我正在向 Angular 发送数据，但记录的其中一个值（关闭日期）为空。我如何在 Angular 中处理这个问题，以便如果 value 为 null ，它会更改为--

  getDetails() {
    this.myService.getFlowerDetails(this.flowerId, this.flowerName).subscribe(
      res => {
        this.flower = res;
        if(this.flower !== undefined){
          this.flowerName = this.flower.flowerName;
          this.flowerId = this.flower.flowerId.toString();
          this.flowerCategory = this.flower.flowerCategory;
          this.recordCreateDate = this.flower.recordCreateDate.toString();
          this.recordClosedDate = this.flower.recordClosedDate.toString(); // this is null in the backend
        }
        else{
          this.flowerName = "--";
          this.flowerId = "--";
          this.flowerCategory = "--";
          this.recordCreateDate = "--";
          this.recordClosedDate = "--";
        }
      }, er => {
    this.throwError = er;
});

我收到以下错误。这不是整个堆栈跟踪（不确定是否需要）

TypeError
​
columnNumber: 17
​
fileName: "http://localhost:4200/main.bundle.js"
​
lineNumber: 1738
​
message: "_this.flower.recordClosedDate is null"

The ||运算符可用于设置默认值，在以下情况下this.flower.recordClosedDate是假的（undefined, null，空字符串，零）：

this.recordClosedDate = (this.flower.recordClosedDate || "--").toString();