Trading method of Java market

Market-trade.java

public List<Sale> trade() {
    List<Sale> sales = new ArrayList<>();
    Set<String> productsInMarket = getProductsInMarket();
    collectMarketInfo();

    // trade each product in succession
    productsInMarket.stream()
        .forEach(productId -> {
            MutableBoolean soldOutOfProduct = new MutableBoolean(false);
            LOGGER.debug("trading product " + productId);
            List<Buyer> buyersInterestedInProduct = getBuyersInterestedInProduct(productId);
            if (buyersInterestedInProduct.size() == 0) {
                LOGGER.info("no buyers interested in product " + productId);
            } else {
                buyersInterestedInProduct.forEach(buyer -> {
                    if (soldOutOfProduct.isFalse()) {
                        LOGGER.debug("  buyer " + buyer.getName() + " is searching for product " + productId);
                        // select the cheapest seller
                        Optional<Seller> cheapestSeller = sellers.stream()
                            .filter(seller -> { return seller.hasProduct(productId);})
                            .sorted((s1, s2) -> 
                                Double.compare(s1.getCheapestSalesOrder(productId).getPrice(),
                                               s2.getCheapestSalesOrder(productId).getPrice()))
                            .findFirst();
                        if (cheapestSeller.isPresent()) {
                            LOGGER.debug("    cheapest seller is " + cheapestSeller.get().getName());
                            List<Sale> newSales = createSale(buyer, cheapestSeller.get(), productId);
                            sales.addAll(newSales);
                            LOGGER.debug("    sales completed");
                        } else {
                            LOGGER.warn("    market sold out of product " + productId);
                            soldOutOfProduct.setTrue();
                        }
                    }
                });
            }
        });
    return sales;
}