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 # Provide an empty string as  the default value if the
 # menu item value isn't provided.
 my $menu_item =  param('menu_item')
               // '';

 # Provide an empty string as  the default value if the
 # menu item value isn't provided.
...

 $_ = param('menu_item');
 my $menu_item = defined() ? $_ : '';

 $menu_item = defined() ? $_ : '' for (param('menu_item');