HHVM Version 3.12.5 / 3.14.3 / 3.18.1

Standalone code, or other way to reproduce the problem

No return from array_unique() with Nested arrays halts and throws array to string conversion

Happens with two nested arrays merged and made unique

array_unique(array_merge($this->_links, $data['links']))

<?php
error_reporting(E_ALL);
$b = array(
  'index.php' =>
  array(
    'relation' => "Start",
    'relType'  => "rel",
    'attribs'  => array(),
  )
);
$c = array(
  'index.php' => 
  array(
    'relation' => "Start",
    'relType'  => "rel",
    'attribs'  => array(),
  )
);
$u = array_unique(array_merge($b,$c));

Related issue #1561

Expected result

Should return a new array without duplicate values ignoring internal array to string conversion notices from the nested arrays

Actual result

no array is returned, just the array to string conversion notice is thrown