NullReferenceException is thrown and Subgraph is not created when converting a node to Subgraph

Reproduction steps:
1. Open the attached “BugRepro” project
2. Open the “Assets/Test.shadergraph” Shader Graph editor
3. Convert a "Maximum" Node to a SubGraph (Right-click > Convert To > Sub-graph)
4. Click Save in the File Dialog
5. Observe the Console window

Expected result: No error is thrown and Subgraph is created
Actual result: “NullReferenceException: Object reference not set to an instance of an object” error is thrown and Subgraph is not created

Reproducible with: 2021.3.38f1, 2022.3.28f1, 6000.0.1f1

Reproducible on: Windows 11
Not reproducible on: No other environment tested