Retroarch fails to save controller config for virtual devices

Description

Controller configs fail to save when using virtual controllers. Due to the nature of my cabinet build, my two "controllers" are actually 4 different players' buttons wired into 2 gamepad boards. To make these compatible with retroarch, I'm creating 4 virtual joysticks with evsieve and mapping events from my 2 controllers to those virtual devices (which is tested and working).

Due to these being virtual devices, they don't have serial numbers, versions, product numbers, or vendor identifiers, which I believe is causing issues with saving configurations within retroarch.

I ran into issues with not being able to manually create configurations for this reason as well.

Expected behavior

To be able to save configurations or autoconfig any joystick, regardless of if it is physical or siimulated

Actual behavior

Retroarch throws errors or crashes, but generally does not save the configuration for the joysticks.

Steps to reproduce the bug

• Create an evsieve script to map events from some input device to a new virtual joystick
• Try to create and save a controller configuration for the new joystick

For reference, my evsieve script can be found here

Version/Commit

You can find this information under Information/System Information

Environment information

• OS: Ubuntu

Start by reproducing the failure with the linked evsieve setup and a virtual joystick, then trace RetroArch's controller configuration and autoconfig handling. Done means a virtual joystick can be configured and saved without errors or crashes, but the issue names no source files or tests to begin with.