Tabular section - ROWID is null

Tabular section - ROWID is null

Hi,
My goal is to update a tabular section. I retrieve the data from the tabular section to test the Creation Date and I need the RowID to update the row. 

CertifRec = Skillrec.getJSON("tabularSections").getJSON("Certifications");
//info "CertifRec " + CertifRec;
for each  RecordList1 in CertifRec
{
CertifCertification = RecordList1.get("Certification");
CertifPassDate = RecordList1.get("PassDate");
CertifAttempt = RecordList1.get("Attempt");
CertifCreatDt = RecordList1.get("Creation_Date");
RowID = RecordList1.get("tabular.ROWID");
        if(CertifCreatDt.isnull())
{
                        // update with the sectionid and the Rowid
                        }
}

I get all the values except the RowID, which is null. I'm using the same code for another form with tabular sections and it works fine. Any suggestions?