Leaving account_id or region parameter empty causes incorrect AWS configuration for some actions.

[jamison-rose]

While using the invoke_lambda action on StackStorm 3.1.0 on Python 3.6.9 I encounter a bug with the following lines:

stackstorm-aws/actions/lib/action.py

Lines 179 to 182 in 6077203

	if 'account_id' in kwargs:
	self.assume_role(kwargs.pop('account_id'))
	if 'region' in kwargs:
	self.credentials['region'] = kwargs.pop('region')

Debugging has shown that actions which do not specify an account_id or a region are still receiving them in the kwargs dict, but with a None value.

I would recommend this change:

account_id = kwargs.pop('account_id', None)
if account_id:
    self.assume_role(account_id)

region = kwargs.pop('region', None)
if region:
    self.credentials['region'] = region

[amanda11]

@jamison-rose I also suffered the same problem. I used your proposed fix and your fix in pull request 104 and it solved the problem.
Is there a PR for your proposed change above?