/// <summary>
 /// Button to add a customer to the list and database.
 /// </summary>
 /// <param name="sender"></param>
 /// <param name="e"></param>
 private void AddCustomerBtn_Click(object sender, EventArgs e)
 {
     if (Validator.IsPresent(firstNameTxtBox) && Validator.IsPresent(lastNameTxtBox) &&
         Validator.IsPresent(addressTxtBox) && Validator.IsPresent(cityTxtBox) &&
         Validator.IsPresent(stateTxtBox) && Validator.IsInt(zipCodeTxtBox.Text))
     {
         Customer customer = new Customer()
         {
             Business         = businessTxtBox.Text,
             ContactFirstName = firstNameTxtBox.Text,
             ContactLastName  = lastNameTxtBox.Text,
             Address          = addressTxtBox.Text,
             City             = cityTxtBox.Text,
             State            = stateTxtBox.Text,
             ZipCode          = Convert.ToInt32(zipCodeTxtBox.Text)
         };
         try
         {
             ProductDb.AddCustomer(customer);
             messageLbl.Text = $"{customer.ContactFirstName} {customer.ContactLastName} was added successfully.";
             ClearTxtBoxes();
         }
         catch (SqlException)
         {
             messageLbl.Text = "Failed to add customer.";
         }
     }
     else
     {
         MessageBox.Show("All fields are required except business.",
                         "Warning",
                         MessageBoxButtons.OK,
                         MessageBoxIcon.Warning);
     }
 }