public static ODocument revokePermissionToUser(String id, Permissions permission, String username) throws UserNotFoundException, RoleNotFoundException, FileNotFoundException, SqlInjectionException, IllegalArgumentException, InvalidModelException {
OUser user=UserService.getOUserByUsername(username);
if (user==null) throw new UserNotFoundException(username);
ODocument doc = getById(id);
if (doc==null) throw new FileNotFoundException(id);
return PermissionsHelper.revoke(doc, permission, user);
}