Angular 7升级：RxJs开关映射和可观测输入的返回类型<；无效>；

此代码在Angular 6中编译和工作：

import { of } from 'rxjs';
import { switchMap } from 'rxjs/operators';

switchMap((term) => {
                if (term.trim().length > 3)
                    return this.searchEntries(term); // <- returns  Observable<void> 

                return of([]);
            })

看起来我必须为switchMap返回ObservableInput，但是如何返回呢

---

非常感谢您的帮助。

感谢@cartant，我通过添加如下返回类型解决了编译时错误：

switchMap((term) : Observable<void | any[]> => {
                if (term.trim().length > 3)
                    return this.searchEntries(term); // <- returns  Observable<void> 

                return of([]);
            })

switchMap（（术语）：可观察=>{
如果（term.trim（）长度>3）
返回此。searchEntries（term）；//为searchEntries添加代码Archentries返回ObservicesName类型脚本限制和解决方法如下：
$ ng version

Angular CLI: 7.0.2
Node: 10.12.0
OS: linux x64
Angular: 7.0.0
... animations, cdk, common, compiler, compiler-cli, core, forms
... http, language-service, platform-browser
... platform-browser-dynamic, router

Package                           Version
-----------------------------------------------------------
@angular-devkit/architect         0.10.2
@angular-devkit/build-angular     0.10.2
@angular-devkit/build-optimizer   0.10.2
@angular-devkit/build-webpack     0.10.2
@angular-devkit/core              7.0.2
@angular-devkit/schematics        7.0.2
@angular/cli                      7.0.2
@ngtools/webpack                  7.0.2
@schematics/angular               7.0.2
@schematics/update                0.10.2
rxjs                              6.3.3
typescript                        3.1.3
webpack                           4.19.1

switchMap((term) : Observable<void | any[]> => {
                if (term.trim().length > 3)
                    return this.searchEntries(term); // <- returns  Observable<void> 

                return of([]);
            })