创建资源失败。预期params.Item为地图

Question

我正在使用aws cdk生成CF模板。在运行cdk deploy时，出现错误 创建资源失败。预期的params.Item为地图。

代码段：

object GenerateItem()
            {
                StringBuilder sb = new StringBuilder("{ \"ApiKey\": { \"S\": \"{apiKey}\" }, \"HmacSigningKey\": { \"S\": \"{hmacKey}\" }, \"Name\": { \"S\": \"{appName}\" } }");

                sb.Replace("{apiKey}", "SuperSecureAPIKey");
                sb.Replace("{hmacKey}", "SuperSecureHMACSigningKey");
                sb.Replace("{appName}", "SuperSecureApp");
                return sb.ToString();
            }

            insertRecord = new AwsSdkCall()
            {
                Service = "DynamoDB",
                Action = "putItem",

                Parameters = new Dictionary<string, object>
                 {
                     { "TableName", Constants.BANKSTATEMENT_API_TOKEN_CONFIG_TABLE_NAME },
                     { "Item", GenerateItem() },
                 },
                PhysicalResourceId = PhysicalResourceId.Of("InitDynamoDbData")
            };

            var ps = new PolicyStatement(new PolicyStatementProps
            {
                Actions = new[] { "*" },
                Resources = new[] { "*" }
            });

            // TODO: Writing to database is not working. "Failed to create resource. Expected params.Item to be a map"
            var dynamodbWriter = new AwsCustomResource(this, Constants.BANKSTATEMENTAPIAUTH_DYNAMODB_WRITER, new AwsCustomResourceProps
            {
                OnCreate = insertRecord,
                Policy = AwsCustomResourcePolicy.FromStatements(new[] { ps })
            });