Azure Activity Log with no “Event Initiated by” value

I was working on Azure Public Cloud and found that there're some events in Activity Log with no Caller value as seen below.

This is an example:

Operation name: Update SQL database
Time stamp: Sun Mar 07 2021 12:27:30 GMT+0700 (Indochina Time)
Event initiated by: - 

The changes was made is earliestRestoreDate (Description :This records the earliest start date and time that restore is available for this database (ISO8601 format).)

I want to know who initiate this event and wondering if this is a kind of system event.

Can someone explain what is this event related to? Thank you!