Graph Toolkit's IPort.Name is null on a variable node's port, so a name-based IsConnectionAllowed rule throws a "NullReferenceException" error

Steps to reproduce:

1. Open the attached "GraphToolkit_Repro" project
2. Open the Graph Toolkit Bug Repro window (Window > Graph Toolkit Bug Repro)
3. Under the "Bugs 3&4" section click the "Build Bug 3/4 graph" button
4. Tick the "BUG 3 ordinary name-based rule" in the GTK Bug Repro window
5. Click the "Reopen" button
6. Observe the Console window

Actual results: Name is null only for variable-node ports. A connection rule that reads it throws a NullReferenceException, and graph validation then stops silently.

Expected results: IPort.Name returns a usable, non-null name for a variable node's output port, consistent with the other port kinds. If null is intended there, it should be documented on IPort.Name.

Reproducible with versions: 6000.6.1f1

Not reproducible with versions: 6000.7.0a6

Can’t test with versions: 6000.0.0f1, 6000.0.83f1, 6000.3.24f1, 6000.5.11f1 (due to functionality not available)

Tested on (OS): MacOS Silicon Tahoe 26.6.2