i have error where i want to choose the product for prescription_line_ids 

File "c:\users\digisolf\pycharmprojects\clinic\acs_hms_pharmacy\model\hms_base.py", line 42, in onchange_product_uom
    price =  self.product_id._get_tax_included_unit_price(
  File "c:\users\digisolf\pycharmprojects\odoo\addons\account\models\product.py", line 163, in _get_tax_included_unit_price
    product_price_unit = product_currency._convert(product_price_unit, currency, company, document_date, round=False)
  File "C:\Users\Digisolf\PycharmProjects\odoo\odoo\addons\base\models\res_currency.py", line 267, in _convert
    assert company, "convert amount from unknown company"
AssertionError: convert amount from unknown company

how to solve this error