ERROR NullInjectorError: R3InjectorError(AppModule)[HttpClient -> HttpClient -> HttpClient]: code example

Example 1: NullInjectorError: No provider for HttpClient!

@NgModule({
...
imports:[ HttpClientModule ]
...
})

Example 2: No provider for HttpClient!

import { HttpClientModule } from '@angular/common/http';

Example 3: NullInjectorError: R3InjectorError HttpClient

// missing import on app.module.ts

import { HttpClientModule } from '@angular/common/http';

@NgModule({
  imports: [
  	HttpClientModule
  ]