svZeroDSolver crashes on Demo Project

[ktbolt]

A user is running a 0D simulation using the Demo Project (https://simtk.org/frs/download_confirm.php/file/5113/DemoProject.zip?group_id=930).

After computing centerlines and setting BCs, etc. the 0D solver is then run and fails with

ERROR: 'NoneType' object has no attribute 'junction_args.

The svZeroDSolver Python code fails in create_junction_blocks with a junction_type = internal_junction but custom_0d_elements_arguments is None.

Looking in the solver_0d.json file I see

        {
            "inlet_vessels": [
                0
            ],
            "junction_name": "J1",
            "junction_type": "internal_junction",
            "outlet_vessels": [
                1
            ]
        },

Simvascular: 2023 05.23 MacOS version.

I've attached the input solver_0d.json file. solver_0d.zip