I found this bug in the process of solving the problem http://stackoverflow.com/questions/33346543/symfony2-how-to-disable-default-voter

Code of method "createRoleHierarchy" in the Symfony/Bundle/SecurityBundle/DependencyInjection/SecurityExtension.php

if (!isset($config['role_hierarchy'])) {
    $container->removeDefinition('security.access.role_hierarchy_voter');
    return;
 }

not work properly, because role_hierarchy contains empty array, when I remove role_hierarchy from my config. so, isset($config['role_hierarchy']) always returns true

And according to comments at #Symfony irc channel from user dantleec1:

yeah, the Configuration class adds the key as an array: https://github.com/symfony/symfony/blob/2.3/src/Symfony/Bundle/SecurityBundle/DependencyInjection/MainConfiguration.php#L136
so I guess NULL resolves to an empty array

To reprocude this bug you need to add code like

var_dump(get_class($voter) . ":" . $result);

to decideConsensus or another decide method of AccessDecisionManager.

I'm use linux, have Symfony version 2.7.5, PHP 5.5.9