diff --git a/system/url.php b/system/url.php
index 3e1de338..76a615d3 100644
--- a/system/url.php
+++ b/system/url.php
@@ -50,7 +50,7 @@ class URL {
 	 * @param  string  $url
 	 * @return string
 	 */
-	public static function to_asset($url)
+	public static function to_asset($url = '')
 	{
 		return static::to($url, false, true);
 	}