Crash if list_price is None
Although list_price field is defined as required in product.template:
https://hg.tryton.org/modules/product/file/tip/product.py#l74
This cannot really be enforced because it is MultiValue. So a product created from company A will have list_price set to NULL on company B.
This will cause crash on get_sale_price() if there needs to be a currency conversion:
https://hg.tryton.org/modules/sale/file/tip/product.py#l158
I think we should:
- Make list_price not required (we already removed the required attribute from cost_price)
- Either do not supply None to currency's compute() or make compute() return None if the value to convert is None