gistfile1.txt

export function ifExists<T>(obj: T | null | undefined, callback: (obj: T) => void) {
  if (exists(obj)) {
    callback(obj as T);
  }
}

addCurrency(currencyType: Currency, amount: number) {
    obj.ifExists(this.model, (dto) => {
      for (const currency of dto.currency) {
        if (currency.first === currencyType) {
          currency.second = Number(amount);
          return;
        }
      }
      const newCurrency = {
        first: currencyType,
        second: Number(amount)
      };
      dto.currency = dto.currency.concat(newCurrency);
    });
  }