private void btnAddUpdatePaid_Click(object sender, System.Windows.RoutedEventArgs e)
		{
            string establishment = txtEstablishment.Text.Trim();
            string concept = txtConcept.Text.Trim();
            string totalAmountText = txtTotalAmount.Text.Trim();
            decimal totalAmount;

            if (AreValidFields(totalAmountText, establishment, concept, out totalAmount) == false)
            {
                return;
            }

            if (_isUpdatePaid)
            {
                _paidToUpdate.Total = totalAmount;
                _paidToUpdate.PaidDate = dtpPaidDate.SelectedDate.Value;
                _paidToUpdate.Establishment = establishment;
                _paidToUpdate.Concept = concept;

                UpdatePaid(_paidToUpdate);
            }
            else
            {
                Model.AmericanExpressPaid paidToAdd = new Model.AmericanExpressPaid()
                {
                    Total = totalAmount,
                    PaidDate = dtpPaidDate.SelectedDate.Value,
                    Establishment = establishment,
                    Concept = concept
                };

                AddPaid(paidToAdd);
            }
		}
        public AddEditAmericanExpressPaidsModal(Model.AmericanExpressPaid paidToUpdate)
		{
			this.InitializeComponent();

            _paidToUpdate = paidToUpdate;
            _isUpdatePaid = _paidToUpdate != null;
            dtpPaidDate.SelectedDate = DateTime.Now;

            if (_isUpdatePaid)
            {
                PrepareWindowForUpdates();
            }
		}