Clicked minus on first item without being set to an item

145068.161 Error MainLoop.cpp:1404: Exception at tick 70295680: The mod Filter assistant (0.0.3) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event filter_assistant::on_gui_click (ID 1)
filter_assistant/scripts/main.lua:312: attempt to perform arithmetic on local 'count' (a nil value)
stack traceback:
filter_assistant/scripts/main.lua:312: in function 'handler'
filter_assistant/scripts/tools.lua:253: in function <filter_assistant/scripts/tools.lua:249>
145068.161 Error ServerMultiplayerManager.cpp:92: MultiplayerManager failed: "The mod Filter assistant (0.0.3) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event filter_assistant::on_gui_click (ID 1)
filter_assistant/scripts/main.lua:312: attempt to perform arithmetic on local 'count' (a nil value)
stack traceback:
filter_assistant/scripts/main.lua:312: in function 'handler'
filter_assistant/scripts/tools.lua:253: in function <filter_assistant/scripts/tools.lua:249>"