[Angular] ControlValueAccessor with formGroup data in child component

Child.ts

import {Component, Input} from '@angular/core'
import { 
  FormControl,
  FormGroup,
  ControlValueAccessor,
  NG_VALUE_ACCESSOR,
  FormBuilder,
  Validator
} from '@angular/forms';

@Component({
  selector: 'my-child',
  template: `
  
  <h1>Child</h1>
  <div [formGroup]="name">
    <input formControlName="firstName">
    <input formControlName="lastName">
  </div>
  `,
  providers: [
    {provide: NG_VALUE_ACCESSOR, useExisting: Child, multi: true}
  ]
})
export class Child implements ControlValueAccessor {
  name: FormGroup;
  constructor(fb: FormBuilder) {
    this.name = fb.group({
      firstName:[''],
      lastName: ['']
    });
  }
  
  writeValue(value: any) {
    if(value) {
        this.name.setValue(value);
    }
  }
  
  registerOnChange(fn: (value: any) => void) {
    this.name.valueChanges.subscribe(fn);
  }
  
  registerOnTouched() {}
}

Parent.ts

import {Component, Input} from '@angular/core'
import { 
  FormControl,
  FormGroup,
  ControlValueAccessor,
  NG_VALUE_ACCESSOR,
  FormBuilder,
  Validator
} from '@angular/forms';

@Component({
  selector: 'my-app',
  template: `
    <div>
      <h4>Hello {{name}}</h4>
      <form [formGroup]="form" (ngSubmit)="sayHello()">
       <input formControlName="name"><br>
       <input formControlName="email"><br>
       <my-child formControlName="username"></my-child>
       <button type="submit">Register</button>
      </form>
      {{form.value | json }}
    </div>
  `
})
export class App {
  form: FormGroup;

  constructor(fb: FormBuilder) {
    this.form = fb.group({
      name:['Angular2 (Release Candidate!)'],
      username: [{firstName: 'First', lastName: 'Last'}],
      email:['My Email']
    });
  }
  
  sayHello() {
    console.log(this.form.value)
  }
}

@MaratMartirosyan999 @sayeduzzamancuet @hknozturk
Looks like creating empty registerOnChange(fn: Function): void solves the issue