$salesKey = 'key';
$sales_items = { $salesKey => {} };

     delete $sale_items->{$salesKey};

print("[", keys(%$sale_items), "]\n");  # []

     doodah()
        if ( $paymentRow->{amount}  < 
             $sale_items->{$salesKey}{amount});

print("[", keys(%$sale_items), "]\n");  # [key]