Node.js 即使DDB键不存在， node Lambda也不会失败，并返回NULL作为结果

我想知道有没有人能帮我排除Node lambda的故障.我有一个带有USER和ACCESS_COUNT键的DDB，但当我使用错误的键参数调用getCommand时，lambda允许它，并成功测试&amp；结果为空.有人知道我错过了什么吗？

// Instrument the AWS SDK client
const client = tracer.captureAWSv3Client(new DynamoDBClient());

//const client = new DynamoDBClient({});
const dynamodb = DynamoDBDocumentClient.from(client);
const table_name = process.env.TABLE_NAME;

const lambdaHandler = async (event, context) => {
    let body;
    let statusCode = 200;
    
    const user = event.user;
    let visit_count = 0;
    
    try {
        const params = {
            TableName: table_name,
            Key: {
                user: user
            }
        };
        
        body = await dynamodb.send(new GetCommand(params));
        if (body.Item) {
            visit_count = body.Item.visit_count;
        }
        visit_count++;
        
        const putParams = {
            TableName: table_name,
            Item: {
                user: user,
                visit_count: visit_count
            }
        };

        body = await dynamodb.send(new PutCommand(putParams));
    
        const message = `Hello ${user}! You have visited us ${visit_count} times.`;
        console.log(message);
        return {
            message: message
        };
    
    }catch (err) {
        statusCode = 400;
        body = err.message;
    } finally {
        body = JSON.stringify(body);
    }
};