Function requiredValidator

packages/forms/src/validators.ts:502–504

(control: AbstractControl)

 * See `Validators.required` for additional information.
 */
export function requiredValidator(control: AbstractControl): ValidationErrors | null {
  return isEmptyInputValue(control.value) ? {'required': true} : null;
}

/**
 * Validator that requires the control's value be true. This validator is commonly