Magento Collection // Join on attribute table

customer_collection_join_attribute_table.php

<?php
/** @var Mage_Customer_Model_Resource_Customer_Collection $collection */
$collection = Mage::getModel('customer/customer')->getCollection();

$collection = $collection->joinAttribute(
    'my_attribute',
    'customer/my_attribute',
    'entity_id',
    null,
    'left'
);

$collection = $collection->addAttributeToFilter('my_attribute', array('null' => true));