Does not repro in Version: 2021.1.8f1.2516
Repros in 2021.2.0b3.3078.7

Repro steps:
1. Create a URP Lit shadergraph in a project with URP
2. Open it and add a custom function node
3. Add an output to the custom function node so it errors
4. Don't plug the custom function node in
5. Save the graph
6. Make a material from the graph
Expected result: the material works because the custom function node wasn't connected to anything
Actual result: the material is pink