How to reproduce:
1. Create a new project using a 3D URP or HDRP template
2. Create a Shader Graph (Create > Shader Graph > URP/HDRP > Lit Shader Graph)
3. Open Shader Graph and undock it
4. Enter Play Mode and exit Play Mode
5. In the Shader Graph window right-click > Create Node
6. Observe the result

Expected result: Node is created
Actual result: Node is not created and the “NullReferenceException: Object reference not set to an instance of an object” error appears

Reproducible with: 14.0.4 (2022.2.2f1), 14.0.6 (2022.2.6f1), 15.0.4 (2023.1.0b3)
Not reproducible with: 10.10.1 (2020.3.44f1), 12.1.10 (2021.3.18f1), 14.0.4 (2022.2.1f1)

Reproduced on: macOS 12.4 (Intel)

Notes:
Reproducible with URP and HDRP
Not reproducible if the Shader Graph window is docked
Not reproducible in State Graph, Script Graph