From 39c8d3e6e1f495b29060ad3a791c6b076ce776ea Mon Sep 17 00:00:00 2001
From: Jordi Boggiano <j.boggiano@seld.be>
Date: Fri, 11 Apr 2014 13:58:47 +0200
Subject: [PATCH] Ignore empty refs

---
 src/Composer/Util/ComposerMirror.php | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/Composer/Util/ComposerMirror.php b/src/Composer/Util/ComposerMirror.php
index ce27af21a..036444d20 100644
--- a/src/Composer/Util/ComposerMirror.php
+++ b/src/Composer/Util/ComposerMirror.php
@@ -21,7 +21,9 @@ class ComposerMirror
 {
     public static function processUrl($mirrorUrl, $packageName, $version, $reference, $type)
     {
-        $reference = preg_match('{^([a-f0-9]*|%reference%)$}', $reference) ? $reference : md5($reference);
+        if ($reference) {
+            $reference = preg_match('{^([a-f0-9]*|%reference%)$}', $reference) ? $reference : md5($reference);
+        }
         $version = strpos($version, '/') === false ? $version : md5($version);
 
         return str_replace(