WordPress Bootstrap Nav Walker Strict Standards Warning

After turning on WordPress Debug on one of my custom themes I noticed a strict standards waring regarding the Navwalker Bootstrap menu.

Error:

Strict Standards: Declaration of… start_lvl() should be compatible with Walker_Nav_Menu::start_lvl(&$output, $depth = 0, $args = Array)

Fix:

change

function start_lvl(&$output, $depth) {

to

function start_lvl(&$output, $depth = 0, $args = array()) {