diff --git a/includes/common.inc b/includes/common.inc
index f153066..7f35c4a 100644
--- a/includes/common.inc
+++ b/includes/common.inc
@@ -494,7 +494,8 @@ function drupal_http_build_query(array $query, $parent = '') {
     }
   }
 
-  return implode('&', $params);
+  $params = array_filter($params);
+  return empty($params) ? NULL : implode('&', $params);
 }
 
 /**