Fix error "undefined method '[]' for nil"

[LisaHader]

After upgrading an application to the current latest version of rails_state_machine (3.1.1) and running my specs, I encountered a lot of errors undefined method '[]' for nil when running the application's specs.

This seems to be caused by the removal of the line @state_machine_state_managers ||= {} in model.rb in the previous version. After creating a model with a state machine through factory bot, the test crashes with the given error message.

After adding the previously removed line of code back in, all my tests are passing as expected.

[makmic]

I'm a bit surprised that it was not enough to set/reset the state machine manager cache only in after_initialize. But I can imagine factory_bot breaking because of it - let's add it back like you suggested 👍