[Ur] Empty transaction

[Urs Wegmann]

Is there a way to create a transaction that does nothing? Something like:
val noop : unit -> transaction unit

The closest thing of this I'm aware of is:
val debug : string -> transaction unit

My use case is:
@foldR2
  [colInfo]
  [source]
  [fn _ => transaction unit]
  (fn [nm :: Name] [t ::_] [rest ::_] [[nm] ~ rest] t s acc =>
    set s t.Default
  )
  (debug "reset sources")
  M.fl
  M.t
  sources

I'm quite new to Ur, so maybe there is a better way to achieve the same.