Do you know what the status "EMPTY" means and how it appears in HRC_TXN_DATA.STATE?

Summary:

I want to know what operation triggers the status "EMPTY" in STATE column on HRC_TXN_DATA table.

Content (please ensure you mask any confidential information):

Hello,

Our client traces the progress of the submission status of Performance Goals by a custom report in which HRC_TXN_DATA table is joined.
Sometimes HRC_TXN_DATA.STATE shows "EMPTY" and I have no idea what the status means nor why it appears.

Does anybody know what the status "EMPTY" in HRC_TXN_DATA.STATE means and what kind of operation triggers this status on the transaction table?
The status "EMPTY" didn't appear after clicking on "Discard" against a pending goal.