Repro steps:
1. Create a subgraph
2. Add a float property to the subgraph's blackboard
3. on the graph inspector choose "Enable custom binding" for the float, save subgraph
4. Create a shadergraph
5. Drag the subgraph into the shadergraph
6. Save the shadergraph and close it
7. delete the subgraph
8. Open the shadergraph
Expected result: it opens and the subgraph node has an error
Actual result: the shadergraph doesn't open, throws error to the console