PHP errors: Declaration of Walker_Nav_Menu_Dropdown should be compatible with Walker_Nav_Menu

Created by: orion434

I receive multiple log entry caused by some incompatible declaration between Walker_Nav_Menu_Dropdown and Walker_Nav_Menu:

Declaration of Walker_Nav_Menu_Dropdown::end_el() should be compatible with 
Walker_Nav_Menu::end_el(&$output, $item, $depth = 0, $args = Array)

Declaration of Walker_Nav_Menu_Dropdown::start_el() should be compatible with 
Walker_Nav_Menu::start_el(&$output, $item, $depth = 0, $args = Array, $id = 0)

Declaration of Walker_Nav_Menu_Dropdown::end_lvl() should be compatible with
Walker_Nav_Menu::end_lvl(&$output, $depth = 0, $args = Array)

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

Type: PHP Strict Standards Line: 0
File: 
/wp-content/plugins/Project-Light-Core-Functionality-ACF-master/inc/nav-menu-dropdown.php