error raised when importance distribution is left empty

[noone1234567]

Hi! Trying to aply pf-boot for my university project. On the website https://probnum.readthedocs.io/en/stable/tutorials/filtsmooth/particle_filtering.html it is written, that linearized_model should be left "empty" so we could use pf-boot. But if I do so I either get a warning that the parameter is required or get an the following error AttributeError: 'NoneType' object has no attribute 'process_initrv_with_data'.