ADR 0279: set says who set a value in its event; a value is changed, not cleared

02-DECISIONS/0279-the-issue-tracker-triages-every-new-issue-and-an-issue-is-ready-when-what-it-depends-on-is-delivered.md

@@ -92,7 +92,7 @@ consolidated schema exist for this store; a reader that does not know a key igno
 
 - `open` takes `severity` and `needs` optionally.
 - A new verb **`set`** changes `severity`, `needs` and `suggested-owner` of an issue, as a person decides; each
-  change is said as the event `set` and kept, with who set it.
+  change is said as the event `set`, with who set it; a value cannot be cleared, only changed.
 - `list` filters on `severity`, `needs` and **`ready`**; its rows carry severity, needs and ready. An agent looking
   for work asks for `severity=minor`, `needs=none`, `ready`.
 - `get` answers `needed-by` and `ready` beside the issue.