如果项目散列键已经存在，如何让DynamoDbContext在保存时抛出异常

using Amazon.DynamoDBv2;
using Amazon.DynamoDBv2.DataModel;
using Amazon.DynamoDBv2.DocumentModel;

// 创建DynamoDB上下文
DynamoDBContext context = new DynamoDBContext(new AmazonDynamoDBClient());

// 创建项目对象
MyItem item = new MyItem
{
    HashKey = "existingKey",
    // 其他属性赋值
};

// 创建条件表达式
Expression conditionExpression = new Expression();
conditionExpression.ExpressionStatement = "attribute_not_exists(HashKey)";

try
{
    // 保存项目，并应用条件表达式
    context.Save(item, new DynamoDBOperationConfig
    {
        ConditionalExpression = conditionExpression
    });
}
catch (ConditionalCheckFailedException ex)
{
    // 处理散列键已存在的异常
    Console.WriteLine("散列键已存在！");
}

import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClientBuilder;
import com.amazonaws.services.dynamodbv2.document.DynamoDB;
import com.amazonaws.services.dynamodbv2.document.Item;
import com.amazonaws.services.dynamodbv2.document.Table;
import com.amazonaws.services.dynamodbv2.model.ConditionalCheckFailedException;

// 创建DynamoDB客户端
AmazonDynamoDB client = AmazonDynamoDBClientBuilder.standard().build();

// 创建DynamoDB对象
DynamoDB dynamoDB = new DynamoDB(client);

// 获取表对象
Table table = dynamoDB.getTable("YourTableName");

// 创建项目对象
Item item = new Item()
    .withPrimaryKey("HashKey", "existingKey")
    // 其他属性赋值
    ;

try {
    // 保存项目
    table.putItem(item);
} catch (ConditionalCheckFailedException ex) {
    // 处理散列键已存在的异常
    System.out.println("散列键已存在！");
}