diff --git a/src/Composer/Json/JsonFile.php b/src/Composer/Json/JsonFile.php
index b514e5b43..cf9dea5f4 100644
--- a/src/Composer/Json/JsonFile.php
+++ b/src/Composer/Json/JsonFile.php
@@ -253,6 +253,9 @@ class JsonFile
      */
     public static function parseJson($json, $file = null)
     {
+        if (null === $json) {
+            return;
+        }
         $data = json_decode($json, true);
         if (null === $data && JSON_ERROR_NONE !== json_last_error()) {
             self::validateSyntax($json, $file);