【PHP7対応】Declaration of walker::start_el(&$output, $item, $depth, $args)の対処方法

[Sun Jul 24 04:12:44 2016] [warn] [client 192.168.0.1] mod_fcgid: stderr: PHP Warning: Declaration of xxx_walker::start_el(&$output, $category, $depth, $args) should be compatible with Walker_Category::start_el(&$output, $category, $depth = 0, $args = Array, $id = 0)

  function start_el(&$output, $category, $depth, $args) {

  
  function start_el( &$output, $category, $depth = 0, $args = array(), $id = 0 ){