Deleting the ID of a gradient in the XML editor leads to a crash when Selectors & CSS dialog is open

Steps to reproduce:

• open Inkscape
• open Selectors & CSS dialog
• open XML editor dialog
• create a rectangle
• set fill to radial gradient
• go to the radial gradient in the defs of the XML editor
• delete the ID attribute

What happened?

Crash: inkscape_backtrace.txt

What should have happened?

No crash :)

Inkscape Version and Operating System:

• Inkscape Version: 1.1-dev (03ae7f7, 2020-01-04)
• Operating System: Windows 10
• Operating System version: 10.0.18362