code: def checkpoints_to_pb(
      checkpoints: Optional[List[Checkpoint]],
  ) -> Optional[List[pb.Checkpoint]]:
      if checkpoints is None:
          return None
      return [checkpoint_to_pb(chk) for chk in checkpoints]
  
imports: import datetime
  import json
  from typing import List, Dict, Any, Optional, MutableMapping
  from google.protobuf import timestamp_pb2
  from .servicepb import keepsake_pb2
  from .experiment import Experiment
  from .checkpoint import Checkpoint, PrimaryMetric, CheckpointList
label_desc: Use image node_id 15 for calling a global function with example usage: checkpoints_to_pb(checkpoints) and returns: unknown, None