Index: wp-includes/functions.php
===================================================================
--- wp-includes/functions.php	(revision 22961)
+++ wp-includes/functions.php	(working copy)
@@ -3589,6 +3589,19 @@
 }
 
 /**
+ * Returns an empty string.
+ *
+ * Useful for returning an empty string to filters easily.
+ *
+ * @since 3.6.0
+ * @see __return_empty_string()
+ * @return string Empty string
+ */
+function __return_empty_string() {
+	return '';
+}
+
+/**
  * Send a HTTP header to disable content type sniffing in browsers which support it.
  *
  * @link http://blogs.msdn.com/ie/archive/2008/07/02/ie8-security-part-v-comprehensive-protection.aspx