System Information
Operating system: Win10
Graphics card: GTX980

Blender Version
Broken: 2.8 RC2

Short description of error
The option "Assign Shortcut" to an Viewport Shading Type gives an error if executed via the assigned Shortcut/Hotkey.

Exact steps for others to reproduce the error

1. Rightclick on any Viewport Shading Button (Wireframe, Solid, Look Dev,...)
2. Select "Assign Shortcut" and assign any shortcut
3. Execute function with shortcut, an Error report appears

There is the "Z" pie menu and the toggle in the Blender Keymap, still direct Shortcuts should be possible if the interface suggests it.