As Broken Maker in the second cycle, I got the "tasty nectar" power, and used it on a starving city. However, later in the same run, there was a null reference error by the "end turn" button that prevented me from advancing turns.

I strongly suspect that this happens when the nectar is used, probably because it's trying to add menace to a non-existent heart of the forest, but I can't totally swear that that's the cause. Re-loading the latest save(after placing the nectar) led to the error, but loading a save before the nectar placement avoided it.