Express Checkout - Can't remove invoice prefix.

[angelleye]

• https://wordpress.org/support/topic/unable-to-clear-invoice-id-prefix-paypal_express-v1-4-3/

I see we are setting a default value for the Invoice Prefix now, which I don't think we did before..??

$this->invoice_id_prefix = $this->get_option('invoice_id_prefix', 'WC-EC');

According to this user if you try to leave the Invoice Prefix blank and save the settings, it keeps replacing the value with the default instead of allowing it to be blank.