php.activerecord

Subject: Different results between PHP 5.6 and 7.0 with the fields from joined table

Hello, i have different results between PHP 5.6 and 7.0 with the fields from joined table.
With PHP 5.6 the empty test is ok, but not with PHP 7.0 :

<?php
// PHP 7.0.7 (Debian Stretch)

$attributes = array(
'order' => 'id DESC',
'limit' => 25
);

$logs = Log::all($attributes);

foreach ($logs as $log)
{
  // $log->user->description = 'bla1';
  $var = $log->user->description;

  // don't print if joined table !
  if ( !empty($log->user->description) )
  {
    print "A:{$log->user->description}";
  }

  // print if $log->user->description is in $var
  if ( !empty($var) )
  {
    print "B:{$log->user->description}";
  }

  // $log->action = 'add';
  //
  // print if field is not joined table
  if ( !empty($log->action) )
  {
    print "Action:{$log->action}";
  }
}

?>

MySQL database :

CREATE TABLE IF NOT EXISTS `users` (
  `id` INTEGER unsigned NOT NULL AUTO_INCREMENT,
  `login` VARCHAR(32) NOT NULL,
  `description` VARCHAR(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci ;

CREATE TABLE IF NOT EXISTS `logs` (
  `id` INTEGER unsigned NOT NULL AUTO_INCREMENT,
  `user_id` INTEGER unsigned NOT NULL,
  `action` ENUM('add','change') DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci ;

INSERT INTO `users` (`id`, `login`, `description`) VALUES
(1, 'fake1', 'bla1'),
(2, 'fake2', NULL);

INSERT INTO `logs` (`id`, `user_id`, `action`) VALUES
(1, 1, 'add'),
(1, 1, NULL);

PHP ActiveRecord models :

//User.php
<?php

class User extends ActiveRecord\Model
{
}

?>

//Log.php
<?php

class Log extends ActiveRecord\Model
{
  static $belongs_to = array(
  array('user')
  );
}

?>

Thank you