Persistence module - anvil.extras

What I’m trying to do:
Hi - I am trying to use the persistence module in anvil extras by following the tutorial/readme docs.
What I’ve tried and what’s not working:
I am not able to make the ‘get’ function work:
anvil.tables.TableError: Column ‘title’ can only be searched with a string (not a simpleObject) in table ‘book’
but if I use the ‘search’ feature, it works fine.
I can implement the persistent_class with search but I’d like to really understand what is the issue with the ‘get’ funciton.
Thanks

Clone link:

As this is anvil-extras specific rather than anvil itself, could you raise this one at: