Steps to repro:
1. open a project (like new URP template)
2. in project tab, right click > create > Shader > Blank Shader Graph
3. in shader graph window > right click > new node
4. in search window, type '[a'

Expected: no exception in console
Actual: exception in console

Repro: 2020.3.1f1, 2021.2.0a11

Workaround: clear error from console and remove regex symbols or enter valid regex in search bar