How to reproduce:
1. Open the attached “SGTest” project
2. Open the “Assets → Test” Shader Graph located in the Project Browser
3. Select any Tab that isn’t the Shader Graph one
4. Enter the Play Mode

Expected result: Play Mode is entered successfully without any abnormal behaviour
Actual result: NullReferenceException is thrown in the Console log

Reproducible with: 15.0.2 (2023.1.0a22), 15.0.3 (2023.1.0a26)
Not reproducible with: 10.10.1 (2020.3.44f1), 12.1.9 (2021.3.17f1), 14.0.5 (2022.2.3f1), 15.0.2 (2023.1.0a21)

Reproduced on: macOS 13.0 (Intel)

Thrown error:
NullReferenceException: Object reference not set to an instance of an object

Note:
- It may reproduce only after the second try