Some old bw2 projects cannot open with `multifunctional` installed in environment

[marc-vdm]

Some bw2 projects cannot open now that multifunctional is non-optional in bw2data. Either bw2data or multifunctional should be able to deal with this right?

  File "/home/marc/.conda/envs/abbeta/lib/python3.11/site-packages/activity_browser/actions/project/project_switch.py", line 51, in run
    bd.projects.set_current(project_name, update=False)
  File "/home/marc/.conda/envs/abbeta/lib/python3.11/site-packages/bw2data/project.py", line 431, in set_current
    project_changed.send(self.dataset)
  File "/home/marc/.conda/envs/abbeta/lib/python3.11/site-packages/blinker/base.py", line 249, in send
    result = receiver(sender, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/marc/.conda/envs/abbeta/lib/python3.11/site-packages/multifunctional/custom_allocation.py", line 258, in update_allocation_strategies_on_project_change
    for key, value in project_dataset.data.get("multifunctional.custom_allocations", {}).items():
                      ^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'get'