       value = f(value)
     value
 toSimpleExtractor = (args) -> (key) -> (value) ->
-  if not value?
+  unless value?
     undefined
   else
     fieldValue = value[key]

      doUnsub()
    doUnsub = obs.subscribeInternal (event) ->
      afterTransaction ->
        if not unsubd
          reply = sink event
          if reply == Bacon.noMore
            unsub()

spys = []
registerObs = (obs) ->
  if spys.length
    unless registerObs.running
      try
        registerObs.running = true
        for spy in spys
