Hi!
This mod is great! But today it caused an error. The drone delivers Explosive cannon shell. Delivery of other items does not cause errors. Here is the text of the error:

Error while running event Long_Range_Delivery_Drones::on_tick (ID 0)
...e_Delivery_Drones__/script/long-range-delivery-drone.lua:331: bad argument

1 of 2 to 'next' (table expected, got nil)

stack traceback:
[C]: in function 'next'
...e_Delivery_Drones__/script/long-range-delivery-drone.lua:331: in function
'deliver_to_target'
...e_Delivery_Drones__/script/long-range-delivery-drone.lua:494: in function 'update'
...e_Delivery_Drones__/script/long-range-delivery-drone.lua: 1256: in function
'update_drones'
...e_Delivery_Drones__/script/long-range-delivery-drone.lua: 1300: in function 'handler'
core/lualib/event_handler.lua:47: in function
<core/lualib/event_handler.lua:45>