I'm migrating some modules from v8 to v10 community.

I have this method:

'@api.multi
    def search_partner_seniat(self):
        """ Check vat of the partner and update iva rate
        """
        self.ensure_one()
        vat = self.vat.upper()
        res = {
            'name': _('The requested contributor does not exist'),
            'vat_subjected': False,
            'vat': vat,
            'wh_iva_agent': False,
            'wh_iva_rate': 0.0
        }

        if 'VE' in vat:
            vat = vat[2:]

        # assumption: both methods in new api style
        if self.env['res.partner'].check_vat_ve(vat): 
            res = self.env['seniat.url']._dom_giver(vat) 
        self.write(res)

        return {
            'type': 'ir.actions.act_window',
            'res_model': 'search.info.partner.seniat',
            'view_mode': 'form',
            'view_type': 'form',
            'res_id': self.id,
            'views': [(False, 'form')],
            'target': 'new',
        }'

It is a button, this method calls for _dom_giver which is like follows:

'@api.multi
    def _dom_giver(self, vat):
        """ Check and validates that the vat is a passport,
        id or rif, to send information to SENIAT and returns the
        partner info that provides.
        """

        url_obj = self.search([], limit=1)
        url1 = url_obj.name + '%s'
        url2 = url_obj.url_seniat + '%s'
        vat = self._validate_rif(vat)
        if vat:
            return self._get_rif(vat, url1, url2)
        else:
            return False'

The error comes on this line 'url1 = url.obj.name + '%s'', the complete traceback:

'Traceback (most recent call last):
  File "/home/kristian/.virtualenvs/odoov10/lib/python2.7/site-packages/odoo-10.0rc1c_20161005-py2.7.egg/odoo/http.py", line 638, in _handle_exception
    return super(JsonRequest, self)._handle_exception(exception)
  File "/home/kristian/.virtualenvs/odoov10/lib/python2.7/site-packages/odoo-10.0rc1c_20161005-py2.7.egg/odoo/http.py", line 675, in dispatch
    result = self._call_function(**self.params)
  File "/home/kristian/.virtualenvs/odoov10/lib/python2.7/site-packages/odoo-10.0rc1c_20161005-py2.7.egg/odoo/http.py", line 331, in _call_function
    return checked_call(self.db, *args, **kwargs)
  File "/home/kristian/.virtualenvs/odoov10/lib/python2.7/site-packages/odoo-10.0rc1c_20161005-py2.7.egg/odoo/service/model.py", line 119, in wrapper
    return f(dbname, *args, **kwargs)
  File "/home/kristian/.virtualenvs/odoov10/lib/python2.7/site-packages/odoo-10.0rc1c_20161005-py2.7.egg/odoo/http.py", line 324, in checked_call
    result = self.endpoint(*a, **kw)
  File "/home/kristian/.virtualenvs/odoov10/lib/python2.7/site-packages/odoo-10.0rc1c_20161005-py2.7.egg/odoo/http.py", line 933, in __call__
    return self.method(*args, **kw)
  File "/home/kristian/.virtualenvs/odoov10/lib/python2.7/site-packages/odoo-10.0rc1c_20161005-py2.7.egg/odoo/http.py", line 504, in response_wrap
    response = f(*args, **kw)
  File "/home/kristian/odoov10/odoo-10.0rc1c-20161005/odoo/addons/web/controllers/main.py", line 866, in call_button
    action = self._call_kw(model, method, args, {})
  File "/home/kristian/odoov10/odoo-10.0rc1c-20161005/odoo/addons/web/controllers/main.py", line 854, in _call_kw
    return call_kw(request.env[model], method, args, kwargs)
  File "/home/kristian/.virtualenvs/odoov10/lib/python2.7/site-packages/odoo-10.0rc1c_20161005-py2.7.egg/odoo/api.py", line 681, in call_kw
    return call_kw_multi(method, model, args, kwargs)
  File "/home/kristian/.virtualenvs/odoov10/lib/python2.7/site-packages/odoo-10.0rc1c_20161005-py2.7.egg/odoo/api.py", line 672, in call_kw_multi
    result = method(recs, *args, **kwargs)
  File "/home/kristian/odoov10/gilda/l10n_ve_fiscal_requirements/wizard/search_info_partner_seniat.py", line 64, in search_partner_seniat
    res = self.env['seniat.url']._dom_giver(vat)  # _dom_giver() should be @api.model
  File "/home/kristian/odoov10/gilda/l10n_ve_fiscal_requirements/model/seniat_url.py", line 215, in _dom_giver
    url1 = url_obj.name + '%s'
TypeError: unsupported operand type(s) for +: 'bool' and 'str''

Originally, _dom_giver method looked like this:

'def _dom_giver(self, cr, uid, vat, context=None):
        """ Check and validates that the vat is a passport,
        id or rif, to send information to SENIAT and returns the
        partner info that provides.
        """
        if context is None:
            context = {}

        url_obj = self.browse(cr, uid, self.search(cr, uid, []))[0]
        url1 = url_obj.name + '%s'
        url2 = url_obj.url_seniat + '%s'
        vat = self._validate_rif(cr, uid, vat, context=None)
        if vat:
            return self._get_rif(cr, uid, vat, url1, url2, context=context)
        else:
            return False'

Any ideas?