kwargs always NoneType

Hi,

in account_fiscal_position_rule_sale/sale.py, method: _fiscal_position_map I always get an error, that kwargs should be a mapping not NoneType.
So I did a little debugging and found out, that kwargs = context.update() always returns None.
I've fixed this with settings kwargs = context first and the update with kwargs.update.

Next problem is, when shop_id is not set, the if-statement does not what it should do:

if context.get('shop_id', False) always returns false...

This fix works for me:

if context.get('shop_id', False) == False:

Please see and review my attached patched. I'm looking forward for comments.

Best regards,

schnere