pages={None:{'items':['a','b'],'next':'t2'},'t2':{'items':[],'next':'t3'},'t3':{'items':['c']}}
def collect():
    token=None;seen=set();out=[]
    while True:
        if token in seen:raise RuntimeError('repeated token')
        seen.add(token);page=pages[token];out.extend(page['items'])
        token=page.get('next')
        if token is None:return out
assert collect()==['a','b','c']
print('PASS: empty middle page does not end fixture inventory; no live Drive request')