code: def empty_checkpoint_pb():
      return pb.Checkpoint(
          id="foo",
          created=pb_convert.timestamp_to_pb(
              datetime.datetime(2020, 12, 7, 1, 13, 29, 192682)
          ),
          step=0,
      )
  
imports: import datetime
  from keepsake import pb_convert
  from keepsake.checkpoint import Checkpoint, PrimaryMetric, CheckpointList
  from keepsake.experiment import Experiment
  from keepsake.servicepb import keepsake_pb2
  from keepsake.project import Project
label_desc: Use image node_id 3 for calling a global function with example usage: empty_checkpoint_pb() and returns: pb