Aurora serverless, RDSDataService, executeStatement() API, " Unexpected key 'formatRecordsAs' found in params" error

Hello, I'm trying to add formatRecordsAs parameter to sqlParams for Aurora serverless RDSDataService (according to RDSDataService SDK) and getting "Unexpected key 'formatRecordsAs' found in params". Here is my code sample:

let sqlParams = {
        secretArn: storeArn.Value,
        resourceArn: dbArn.Value,
        database: dbSchema.Value,
        formatRecordsAs: 'JSON'
      };
sqlParams.sql = `select ...`;
let data = await RDS.executeStatement(sqlParams).promise();

Note that without "formatRecordsAs" parameter all works just fine. I double checked with RDSDataService SDK docs and didn't find any inconsistency in my code. What I might possibly missing here???

Thank you,

Victor.