Product getProductById(String productID);

public Product getProductById(String productId) {
    Product productById = null;
    
    for(Product product : listOfProducts) {
      if(product!=null && product.getProductId()!=null && product.getProductId().equals(productId)){
        productById = product;
        break;
      }
    }
    
    if(productById == null){
      throw new IllegalArgumentException("No products found with the product id: "+ productId);
    }
    
    return productById;
}