我正在使用ng-bootstrap模态组件，但它没有显示

Question

当我尝试显示它时，它会给出以下错误：

core.es5.js:1020 ERROR Error: Uncaught (in promise): 0
    at resolvePromise (zone.js:712) [angular]
    at NgbModalRef._reject (zone.js:638) [angular]
    at NgbModalRef.dismiss (modal-ref.js:54) [angular]
    at :4200/vendor.bundle.js:45949:82 [angular]
    at SafeSubscriber.schedulerFn [as _next] (core.es5.js:3647) [angular]
    at SafeSubscriber.__tryOrUnsub (Subscriber.js:239) [angular]
    at SafeSubscriber.next (Subscriber.js:186) [angular]
    at Subscriber._next (Subscriber.js:126) [angular]
    at Subscriber.next (Subscriber.js:90) [angular]
    at EventEmitter.Subject.next (Subject.js:55) [angular]
    at EventEmitter.emit (core.es5.js:3621) [angular]
    at NgbModalWindow.dismiss (modal-window.js:21) [angular]
    at NgbModalWindow.backdropClick (modal-window.js:13) [angular]
    at Object.eval [as handleEvent] (NgbModalWindow_Host.html:1) 

它正在工作，它突然停止工作！ 这是官方文件https://ng-bootstrap.github.io/#/components/modal