error from generate_from_string method for BART

Hi, I'm attempting to run the BART model example as given in the readme:

import torch
from transformers import BartTokenizer
from bart import MyBart

base_model = "facebook/bart-large"
unifiedqa_path = "unifiedQA-uncased/best-model.pt" # path to the downloaded checkpoint

tokenizer = BartTokenizer.from_pretrained(base_model)
model = MyBart.from_pretrained(base_model, state_dict=torch.load(unifiedqa_path))
model.eval()

x = model.generate_from_string("Which is best conductor? \\n (A) iron (B) feather", tokenizer=tokenizer)

The .from_pretrained line executes fine but the .generate_from_string(..) line errors out with the error:

TypeError: forward() got an unexpected keyword argument 'past_key_values'

I tried using the run_model(..) method from the main git page and it gives exactly the same error.

Any idea what might be causing this and how to fix it?

I am using python 3.85 with transformers 4.4.2 and pytorch 1.7.1