export function coerceDateProperty<D>(adapter: DateAdapter<D>, value: any): D | null {
  if (typeof value === 'string') {
    if (value == '') {
      value = null;
    } else {
      value = adapter.fromIso8601(value) || value;
    }
  }
  if (value == null || adapter.isDateInstance(value)) {
    return value;
  }
  throw Error(`Datepicker: Value must be either a date object recognized by the DateAdapter or ` +
              `an ISO 8601 string. Instead got: ${value}`);
}

 french() {
   this._adapter.setLocale('fr');
 }