Description:
------------
PHP 5.6.0 added a third argument to array_filter, $flag, which can accept one of the integer constants ARRAY_FILTER_USE_KEY or ARRAY_FILTER_USE_BOTH. When the former is specified, the key is passed as the sole argument to the callback; when the latter is specified, the value and the key, in that order, are passed to the callback.

Under the current master branch, the $flag is ignored.

Test script:
---------------
$toFilter = array('foo' => 'bar', 'fiz' => 'buz');
$filtered = array_filter($toFilter, function ($value, $key) {
    if ($value === 'buz'
        || $key === 'foo'
    ) {
        return false;
    }
    return true;
}, ARRAY_FILTER_USER_BOTH);
var_export($filtered);

Expected result:
----------------
array()

Actual result:
--------------
Missing argument 2 for {closure}()