[6.1] TypeError: 'NoneType' object is not iterable

On 6.1,

* install hr_expense_line_supplier and account_tax_expense_included
* Check included in expense on a tax
* Create an expense sheet line with a product using the previous tax
* Confirm and approve the expense sheet
* Generate the invoice

I get:

Server Traceback (most recent call last):
  File "/home/max/openerp/web/6.1/addons/web/common/http.py", line 593, in send
    return openerp.netsvc.dispatch_rpc(service_name, method, args)
  File "/home/max/openerp/server/6.1/openerp/netsvc.py", line 360, in dispatch_rpc
    result = ExportService.getService(service_name).dispatch(method, params)
  File "/home/max/openerp/server/6.1/openerp/service/web_services.py", line 586, in dispatch
    res = fn(db, uid, *params)
  File "/home/max/openerp/server/6.1/openerp/osv/osv.py", line 167, in execute_kw
    return self.execute(db, uid, obj, method, *args, **kw or {})
  File "/home/max/openerp/server/6.1/openerp/osv/osv.py", line 121, in wrapper
    return f(self, dbname, *args, **kwargs)
  File "/home/max/openerp/server/6.1/openerp/osv/osv.py", line 176, in execute
    res = self.execute_cr(cr, uid, obj, method, *args, **kw)
  File "/home/max/openerp/addons/6.1/audittrail/audittrail.py", line 495, in execute_cr
    return fct_src(cr, uid, model, method, *args)
  File "/home/max/openerp/server/6.1/openerp/osv/osv.py", line 164, in execute_cr
    return getattr(object, method)(cr, uid, *args, **kw)
  File "/home/max/openerp/addons/6.1/hr_expense/hr_expense.py", line 138, in invoice
    wf_service.trg_validate(uid, 'hr.expense.expense', id, 'invoice', cr)
  File "/home/max/openerp/server/6.1/openerp/workflow/wkf_service.py", line 124, in trg_validate
    res2 = instance.validate(cr, id, ident, signal)
  File "/home/max/openerp/server/6.1/openerp/workflow/instance.py", line 48, in validate
    workitem.process(cr, witem, ident, signal, force_running, stack=stack)
  File "/home/max/openerp/server/6.1/openerp/workflow/workitem.py", line 61, in process
    ok = _split_test(cr, workitem, activity['split_mode'], ident, signal, stack)
  File "/home/max/openerp/server/6.1/openerp/workflow/workitem.py", line 176, in _split_test
    _join_test(cr, t[0], t[1], ident, stack)
  File "/home/max/openerp/server/6.1/openerp/workflow/workitem.py", line 184, in _join_test
    create(cr,[activity], inst_id, ident, stack)
  File "/home/max/openerp/server/6.1/openerp/workflow/workitem.py", line 41, in create
    process(cr, res, ident, stack=stack)
  File "/home/max/openerp/server/6.1/openerp/workflow/workitem.py", line 53, in process
    result = _execute(cr, workitem, activity, ident, stack)
  File "/home/max/openerp/server/6.1/openerp/workflow/workitem.py", line 128, in _execute
    id_new = wkf_expr.execute(cr, ident, workitem, activity)
  File "/home/max/openerp/server/6.1/openerp/workflow/wkf_expr.py", line 68, in execute
    return _eval_expr(cr, ident, workitem, activity['action'])
  File "/home/max/openerp/server/6.1/openerp/workflow/wkf_expr.py", line 58, in _eval_expr
    ret = eval(line, env, nocopy=True)
  File "/home/max/openerp/server/6.1/openerp/tools/safe_eval.py", line 241, in safe_eval
    return eval(test_expr(expr,_SAFE_OPCODES, mode=mode), globals_dict, locals_dict)
  File "", line 1, in <module>
  File "/home/max/openerp/server/6.1/openerp/osv/orm.py", line 368, in function_proxy
    return attr(self._cr, self._uid, [self._id], *args, **kwargs)
  File "/home/max/openerp/canada/6.1/hr_expense_line_supplier/hr_expense_line_supplier.py", line 56, in action_invoice_create
    for i in l.partner_id.property_account_position.tax_ids:
TypeError: 'NoneType' object is not iterable