I have the following code that is throwing a exception:

This code is inside account module.

It throws the exception:

  File "/home/danimar/projetos/odoo/odoo-eight/addons/account/account_invoice.py", line 1220, in _compute_price
    taxes = self.invoice_line_tax_id.compute_all(price, self.quantity, product=self.product_id, partner=self.invoice_id.partner_id)
  File "/home/danimar/projetos/odoo/odoo-eight/openerp/api.py", line 235, in wrapper
    return new_api(self, *args, **kwargs)
ParseError: "'NoneType' object is not callable" while parsing

Why this is happening?

I have two classes that inherit from account.tax but both are still using old api.