DB fails to connect in scheduler when no explicit credential is in the connection string

[onetwomani]

Describe the bug
The scheduler fails to connect to the db after starting up if the connection string does not provide an explicit password.
Filing reference for similar issue [https://github.com/web2py/web2py/issues/2335]

To Reproduce
Steps to reproduce the behavior:

With a postgresql database, create a .pgpass file that stores the db credential such
Launch application with scheduler using
python web2py.py -K
See error
web2py Web Framework
Created by Massimo Di Pierro, Copyright 2007-2020
Version 2.20.4-stable+timestamp.2020.05.02.22.03.36
Database drivers available: psycopg2, imaplib, pymysql, pyodbc
starting single-scheduler for "app"...
Exception in thread Thread-1:
Traceback (most recent call last):
File "/usr/local/lib/python3.8/threading.py", line 932, in _bootstrap_inner
self.run()
File "/var/www/web2py/gluon/scheduler.py", line 792, in run
self.send_heartbeat(counter)
File "/var/www/web2py/gluon/scheduler.py", line 1175, in send_heartbeat
self.db_thread = DAL(
File "/var/www/web2py/gluon/packages/dal/pydal/base.py", line 208, in call
obj = super(MetaDAL, cls).call(*args, **kwargs)
File "/var/www/web2py/gluon/packages/dal/pydal/base.py", line 524, in init
raise RuntimeError(
RuntimeError: Failure to connect, tried 5 times:
Traceback (most recent call last):
File "/var/www/web2py/gluon/packages/dal/pydal/base.py", line 506, in init
self._adapter = adapter(**kwargs)
File "/var/www/web2py/gluon/packages/dal/pydal/adapters/postgres.py", line 28, in call
return AdapterMeta.call(cls, *args, **kwargs)
File "/var/www/web2py/gluon/packages/dal/pydal/adapters/init.py", line 41, in call
obj = super(AdapterMeta, cls).call(*args, **kwargs)
File "/var/www/web2py/gluon/packages/dal/pydal/adapters/postgres.py", line 58, in init
super(Postgre, self).init(
File "/var/www/web2py/gluon/packages/dal/pydal/adapters/base.py", line 417, in init
super(SQLAdapter, self).init(*args, **kwargs)
File "/var/www/web2py/gluon/packages/dal/pydal/adapters/base.py", line 86, in init
self.initialize()
File "/var/www/web2py/gluon/packages/dal/pydal/adapters/postgres.py", line 78, in initialize
password = self.credential_decoder(m.group("password"))
File "/var/www/web2py/gluon/packages/dal/pydal/base.py", line 454, in
credential_decoder = lambda cred: unquote(cred)
File "/usr/local/lib/python3.8/urllib/parse.py", line 634, in unquote
if '%' not in string:
TypeError: argument of type 'NoneType' is not iterable

Expected behavior
Scheduler task should run...