code: def end(self, now=None):
      if now is None:
          now = time.time()
      self._end = now
  
imports: import time
  from contextlib import contextmanager
  from metaflow.sidecar import Message, MessageTypes, Sidecar
label_desc: Use image node_id 3 for calling the Timer obj's underlying member method code with example usage: obj.end(now) without return types