I ran into a bug where I was feeding a random signal into a stop, and was then rewiring it. When I removed one of the wires I got a crash and this error:

The mod Programmable Train Stop Naming (1.0.0) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event programmable-train-stop-naming::on_tick (ID 0)
programmable-train-stop-naming/control.lua:197: bad argument #1 of 2 to 'ipairs' (table expected, got nil)
stack traceback:
[C]: in function 'ipairs'
programmable-train-stop-naming/control.lua:197: in function 'remove_signal'
programmable-train-stop-naming/control.lua:226: in function 'remove_expected_control_signals'
programmable-train-stop-naming/control.lua:153: in function 'update_train_stop_setting_from_signals'
programmable-train-stop-naming/control.lua:136: in function <programmable-train-stop-naming/control.lua:129>

ok it actually looks like it happens when I switch to a signal that has 1 tick of no signal

Thanks for reporting this.
I uploaded an update that should fix that.

I also should mention that there is a logic that ignores symbols that are used in the train stop circuite logic for naming.