I was testing out dynamic naming and was sending a stone signal to the station. The station was also set to enable when stone > 0 and used the stone signal to set the train limit. If I changed enable to "anything > 0" and then deleted the train limit variable, I got the crash report below. I also noticed that with stone as the enable/disable signal and limit signal, it wasn't appending the signal into the station name. I have a save file from before the crash if it would be helpful.

Error while running event programmable-train-stop-naming::on_tick (ID 0)
programmable-train-stop-naming/control.lua:212: attempt to index local 'signal' (a nil value)
stack traceback:
programmable-train-stop-naming/control.lua:212: in function 'remove_signal'
programmable-train-stop-naming/control.lua:249: in function 'remove_expected_control_signals'
programmable-train-stop-naming/control.lua:164: in function 'update_train_stop_setting_from_signals'
programmable-train-stop-naming/control.lua:150: in function <programmable-train-stop-naming/control.lua:135>