About RECOVERY_DID_LIST_HASH, where it come from during first creation

I found the wallet cli client (cmds/wallet.py) is initialize first DID wallet with empty backup_ids, and then through some methods until passed to RECOVERY_DID_LIST_HASH of did_innerpuz. I assume this field should empty. However, with on-chain analysis, obviously, there is something in this RECOVERY_DID_LIST_HASH field.

My question is what is that and how this value created?

PS: with assigning (), I can create DID successfully, but I assume it is really important that I should not miss it.