Filter with an array param

wp-signup.php

<?php

/**
 * Allow definition of default variables
 *
 * @since MU
 *
 * @param array $user_data The user data to define {
 *     @type string $user_name  The username
 *     @type string $user_email The user's email
 *     @type array  $errors
 * }
 */
$filtered_results = apply_filters('signup_user_init', array('user_name' => $user_name, 'user_email' => $user_email, 'errors' => $errors ));