How to reproduce:
1. Open the attached "ErrorsTest" project
2. Open any Shader Graph (Assets -> ShaderGraphs)
3. With the Shader Graph opened, enter the Play Mode
4. Observe the Console

Expected results: No errors are thrown
Actual results: NullReferenceException errors are thrown

Reproducible with: 6000.0.36f1, 6000.1.0b4
Not reproducible with: 2022.3.57f1

Reproducible on: macOS Sequoia 14.1 (M1)
Not reproducible on: No other environment tested

Notes:
- Can't find a proper regression point due to the bug most likely depending on the ShaderGraph package version
- The errors are gone when entering the Play Mode for the second time

First lines of error:
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.ShaderGraph.Drawing.BlackboardController.InitializeViewModel (System.Boolean useDropdowns) (at ./Library/PackageCache/com.unity.shadergraph@bc9b3b2d3f8f/Editor/Drawing/Controllers/BlackboardController.cs:455)