The mod Transport Drones (0.7.5) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Transport_Drones::on_tick (ID 0)
'count': real number expected got nil.
stack traceback:
Transport_Drones/script/depots/mining_depot.lua:99: in function 'update_contents'
Transport_Drones/script/depots/mining_depot.lua:106: in function 'update'
Transport_Drones/script/depot_common.lua:379: in function 'update_depots'
Transport_Drones/script/depot_common.lua:387: in function 'handler'
core/lualib/event_handler.lua:47: in function <core/lualib/event_handler.lua:45>
stack traceback:
[C]: in function 'set_signal'
Transport_Drones/script/depots/mining_depot.lua:99: in function 'update_contents'
Transport_Drones/script/depots/mining_depot.lua:106: in function 'update'
Transport_Drones/script/depot_common.lua:379: in function 'update_depots'
Transport_Drones/script/depot_common.lua:387: in function 'handler'
core/lualib/event_handler.lua:47: in function <core/lualib/event_handler.lua:45>

same crash just happened on my game when i put a depot reader on a mining depot (i tried this since the mining depot also acts as a supply depot and can't be read directly by conecting a wire), using factorio 0.18.29 and Transport Drones 0.7.5 (and yes, i really checked that it is the newest version since the other report also referred to 0.7.5 and is already 6 days old while i usually expect to see 7 updates per week, lol :-) :

The mod Transport Drones (0.7.5) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Transport_Drones::on_tick (ID 0)
'count': real number expected got nil.
stack traceback:
Transport_Drones/script/depots/mining_depot.lua:99: in function 'update_contents'
Transport_Drones/script/depots/mining_depot.lua:106: in function 'update'
Transport_Drones/script/depot_common.lua:379: in function 'update_depots'
Transport_Drones/script/depot_common.lua:387: in function 'handler'
core/lualib/event_handler.lua:47: in function <core/lualib/event_handler.lua:45>
stack traceback:
[C]: in function 'set_signal'
Transport_Drones/script/depots/mining_depot.lua:99: in function 'update_contents'
Transport_Drones/script/depots/mining_depot.lua:106: in function 'update'
Transport_Drones/script/depot_common.lua:379: in function 'update_depots'
Transport_Drones/script/depot_common.lua:387: in function 'handler'
core/lualib/event_handler.lua:47: in function <core/lualib/event_handler.lua:45>

after some more updates, i tried again and it no longer crashes, but still seems to be buggy:

when placing the reader, i see a message that it has been connected,
BUT the depot reader doesn't read the type of ore that is mined and also no values.
when i click on it, only a constant combinator with a single slot opens,
and when i try to set anything on that one slot, it is automatically overwritten with <nothing>.