pydal do not support mongodb 4.4+

[Alex-echo]

Describe the bug
pydal not support mongodb 4.4+

To Reproduce
Steps to reproduce the behavior:
when mongodb 4.2 upgrade to mongodb 4.4, web2py pydal (DAL) can‘t work: select tables expect values but return keys。
(to CRUD mongodb directly in python with pymongo , It works fine).

===
env：
web2py 2.22.3
pymongo 3.12.3
mongodb 4.4.14
suse 12 sp5
python 2.7.17