yeah all of the resources tracked by the game (food, gold, etc.) are in resources in the globals file.
i noticed today if i bought an incubator then tried to use it i got a similar issue. however, buying the incubator, saving the game and then restarting seemed to fix it. again it seems like the object is not initialized (at least that is what i would guess with other languages I have worked with). gdscript is not the best language and the lack of error handling (along with other short comings) really makes proper code design impossible