Trying to place order from Online Store or via PlaceOrderAndAuthorize_API API request returns the error:
comparison with NULL currency value error
Handling fee is enabled for the payment method which is used.
Handling Fee Upper or Lower Limits are empty.
Set the values for Handling Fee Upper Limit and/or Handling Fee Lower Limit under System > Settings > Payments Processing > [choose payment system] > Edit, save the settings.