Thanks for looking!
I found a bug, where it won't let you blank the fuel price.
If you set to false FUEL_GET_LIVE_PRICE (looks like you did), and set the fuel price as blank, it will then pick up that default price.
I fixed the bug where it default it to 0 when it's blank. Though, I might say if it's 0, and LIVE_PRICE is false, then it should use that default price? Would that be ok?
I'll add an accept button