– open the file /components/com_mtree/Savant2/Savant2-Plugin_ahreflisting.php
– go to line 21,
– remove the & sign just before $link, so that line 21 reads :
Code:

function plugin($link, $link_name, $attr=null, $show=null, $visit=0)

instead of
Code:

function plugin(&$link, $link_name, $attr=null, $show=null, $visit=0)

– save file and it should work