ng validation for ionic checkbox

export class RegisterComponent {

  registerForm: FormGroup;
  email = new FormControl('', [Validators.required]);
  password = new FormControl('', [Validators.required]);
  termsAndConditions = new FormControl(undefined, [Validators.required]);

  constructor(private formBuilder: FormBuilder) {
    this.registerForm = this.formBuilder.group({
      'email': this.email,
      'password': this.password,
      'termsAndConditions': this.termsAndConditions
    }, {validator: this.checkCheckbox });
  }
  public checkCheckbox(c: AbstractControl){
  if(c.get('termsAndConditions').value == false){
    return false;
  }else return true;
}
}