Impacted versions:
- 8.0

Steps to reproduce:
1. open Accounting / Configuration / Taxes / Tax Codes
2. open any Tax Code
3. press Print / Account Tax

Current behavior:

QWebException: "chart_tax_id" while evaluating
"get_lines(data['form']['based_on'], data['form']['company_id'], data['form']['chart_tax_id'])"
Details: http://paste.ubuntu.com/12689915/

Expected behavior:
- Tax Code report

Test on:
- different 8.0 instances
- runbot: http://105817-8-0-6b6d73.runbot8.odoo.com/web

addons/account/report/report_vat.py
if context is None:
            context = {}
        if account_list is None:
            account_list = []
        if period_list is None:
            period_list = []
        res = []
        obj_tc = self.pool.get('account.tax.code')
        for account in account_list:
            ids = obj_tc.search(self.cr, self.uid, [('id','=', account[1].id)], context=context)
            code = {}
            for period_ind in period_list:
                context2 = dict(context, period_id=period_ind, based_on=based_on)
                record = obj_tc.browse(self.cr, self.uid, ids, context=context2)[0]
                if not code:
                    code = {
                        'id': record.id,
                        'name': record.name,
                        'code': record.code,
                        'sequence': record.sequence,
                        'sum_period': 0,
                    }
                code['sum_period'] += record.sum_period
            res.append((account[0], code))
        return res
    def _get_currency(self, form, context=None):