Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/odoo/http.py", line 640, in _handle_exception
    return super(JsonRequest, self)._handle_exception(exception)
  File "/usr/lib/python2.7/dist-packages/odoo/http.py", line 677, in dispatch
    result = self._call_function(**self.params)
  File "/usr/lib/python2.7/dist-packages/odoo/http.py", line 333, in _call_function
    return checked_call(self.db, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/odoo/service/model.py", line 101, in wrapper
    return f(dbname, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/odoo/http.py", line 326, in checked_call
    result = self.endpoint(*a, **kw)
  File "/usr/lib/python2.7/dist-packages/odoo/http.py", line 935, in _call_
    return self.method(*args, **kw)
  File "/usr/lib/python2.7/dist-packages/odoo/http.py", line 506, in response_wrap
    response = f(*args, **kw)
  File "/usr/lib/python2.7/dist-packages/odoo/addons/web/controllers/main.py", line 894, in call_button
    action = self._call_kw(model, method, args, {})
  File "/usr/lib/python2.7/dist-packages/odoo/addons/web/controllers/main.py", line 882, in _call_kw
    return call_kw(request.env[model], method, args, kwargs)
  File "/usr/lib/python2.7/dist-packages/odoo/api.py", line 689, in call_kw
    return call_kw_multi(method, model, args, kwargs)
  File "/usr/lib/python2.7/dist-packages/odoo/api.py", line 680, in call_kw_multi
    result = method(recs, *args, **kwargs)
  File "<decorator-gen-146>", line 2, in send_fiscal_printer_action
  File "/usr/lib/python2.7/dist-packages/odoo/api.py", line 369, in loop
    result = [method(rec, *args, **kwargs) for rec in self]
  File "/usr/lib/python2.7/dist-packages/odoo/addons/fpi/models/models.py", line 92, in send_fiscal_printer_action
    self.printer_id = printer.id
  File "/usr/lib/python2.7/dist-packages/odoo/fields.py", line 2477, in _get_
    return record.ensure_one()._ids[0]
  File "/usr/lib/python2.7/dist-packages/odoo/models.py", line 4820, in ensure_one
    raise ValueError("Expected singleton: %s" % self)
ValueError: Expected singleton: fpi.printer(2, 3)