Description:
------------
If I curl a webpage that returns standard headers and no content, using CULOPT_RETURNTRANSFER = true to get the content returned on curl_exec, I get an empty string in $return_value from the call

$return_value = curl_exec($url);

However, if I do the same using curl_multi functions, I get a "null" value instead of the expected empty string.

$return_value = curl_multi_getcontent($ch);

Tested using the exact same curl options block, against two requests (one of which returned some text, and the other which was an empty page). The multi_curl against the empty page gives a NULL value for $return_value, which is incorrect, and should be an empty string.

Test script:
---------------
<?php
$url = 'http://bargainlight.com/empty.php';
$url2 = 'http://bargainlight.com/nonempty.php';

$curl_options =  array(
    CURLOPT_FOLLOWLOCATION => true,
    CURLOPT_MAXREDIRS => 3,
    CURLOPT_RETURNTRANSFER => true
);

$ch_1 = curl_init();
$ch_2 = curl_init();
$ch_3 = curl_init();
$ch_4 = curl_init();
curl_setopt_array($ch_1, $curl_options);
curl_setopt($ch_1, CURLOPT_URL, $url);
curl_setopt_array($ch_2, $curl_options);
curl_setopt($ch_2, CURLOPT_URL, $url);
curl_setopt_array($ch_3, $curl_options);
curl_setopt($ch_3, CURLOPT_URL, $url2);
curl_setopt_array($ch_4, $curl_options);
curl_setopt($ch_4, CURLOPT_URL, $url2);

$multi_handle = curl_multi_init();
curl_multi_add_handle($multi_handle, $ch_1);
curl_multi_add_handle($multi_handle, $ch_3);

$r2 = curl_exec($ch_2);
$r4 = curl_exec($ch_4);

do {
    curl_multi_exec($multi_handle, $running);
    curl_multi_select($multi_handle);
} while ($running > 0);

$r1 = curl_multi_getcontent($ch_1);
$r3 = curl_multi_getcontent($ch_3);

var_dump($r1);
var_dump($r2);
var_dump($r3);
var_dump($r4);


Expected result:
----------------
r1 should be not null