call from form_valid.
        @form: it is form of form_valid (type: form)
        @field: name of the form field referring to the brigde (type: string)
        @model: form's model (type class)
        @related_field: name of the related_name of the brigde (type: string)
        @error_message: list of message errors (type list)
            two items, example:
            ["The selected entry is already a storage, select another entry!",
            "The selected entry is not available anymore, please, try again!"]

def form_valid_bridge(self, form, field, model, related_field, error_message):
        """
        call from form_valid.
        @form: it is form of form_valid (type: form)
        @field: name of the form field referring to the brigde (type: string)
        @model: form's model (type class)
        @related_field: name of the related_name of the brigde (type: string)
        @error_message: list of message errors (type list)
            two items, example:
            ["The selected entry is already a storage, select another entry!",
            "The selected entry is not available anymore, please, try again!"]
        """
        # get instance of selected external object
        external = form.cleaned_data[field]
        related_object = get_external_model(model).objects.filter(pk=external.pk).first()
        if related_object:
            # form valid
            try:
                with transaction.atomic():
                    result = super(GenCreateBridge, self).form_valid(form)
                    if get_external_model(model).objects.filter(**{
                            "pk": external.pk,
                            "{}__isnull".format(related_field): False
                            }).exists():
                        errors = form._errors.setdefault(field, ErrorList())
                        errors.append(error_message[0])
                        raise CodenerixException()
                    else:
                        setattr(related_object, related_field, form.instance)
                        related_object.save()
                        if hasattr(self.object, 'CDNX_refresh_permissions_CDNX'):
                            self.object.CDNX_refresh_permissions_CDNX()
                # Return the object already saved properly
                answer = HttpResponseRedirect(self.get_success_url())
            except CodenerixException:
                answer = super(GenCreateBridge, self).form_invalid(form)
            except IOError as e:
                errors = form._errors.setdefault("codenerix_external_field", ErrorList())
                errors.append(e)
                answer = super(GenCreateBridge, self).form_invalid(form)
        else:
            errors = form._errors.setdefault(field, ErrorList())
            errors.append(error_message[1])
            answer = super(GenCreateBridge, self).form_invalid(form)

        # Return
        return answer