How to reproduce:
1. Create a new URP Template project
2. Import the attached project named "ReproGraph_1298867"
3. Observe the imported asset in the Project window

Expected result: The graph is imported and can be opened using the ShaderGraph Editor
Actual result: The graph fails to import properly and cannot be edited using ShaderGraph

Reproducible wtih 10.0.0-preview.27(2020.2.0b8), 10.2.2(2020.2.1f1), 11.0.0(2021.1.0a10)
Not reproducible with: 7.5.2(2019.4.17f1), 8.3.1(2020.1.17f1)
Could not test with: 2018.4.30f1(ShaderGraph was in early preview)

Notes:
1. If the Active Master node is changed to the one which receives the Custom Function Node's output, the graph will be imported properly. Alternatively, if the Edge connected to the Custom Node's input is deleted, the graph will be imported properly as well