I need to write an automation for when a custom field changes to send a slack message only on 2nd and subsequent changes. For example, field name is Quarter committed. It remains empty for a while. When they are ready to commit to a quarter they enter a value. No slack message should be sent. After this, then any change including back to empty needs to send a slack message. Is there a way to tell when the value has changed the first time without checking "empty"? Like looping through the history of a field?