Error openning buy menu

Error while running event BlackMarket2::on_gui_click (ID 1)
__BlackMarket2__/control.lua:1001: attempt to index field '?' (a nil value)
stack traceback:
	__BlackMarket2__/control.lua:1001: in function 'build_menu_objects'
	__BlackMarket2__/control.lua:3358: in function <__BlackMarket2__/control.lua:3076>

It in trading tank(buy) if i click to open the menu for choose what to buy