Hi,

For this what you can do is that, inherit the account.move and super the function of the POST) action_post) button and check whether the end user entered the journal items(line_ids), if lines_ids is not entered you can return a warning message.

def action_post(self):

    res = super(classname, self).action_post()

    if not self.line_ids:

        # return warning message

        raise ValidationError(_("No Journal Items"))

    return res

The code is just typed , not tested, so check and make necessary changes

Thanks