message: Skip mongo write if no new messages to checkpoint
  It's an invalid operation to do a batch insert with an empty array
diff: @@ -188,6 +188,8 @@ export class ScribeLambda extends SequencedLambda {
  // will no longer be referenced.
  const inserts = this.pendingCheckpointMessages.toArray();
  this.pendingCheckpointMessages.clear();
  +
  + if (inserts.length > 0) {
  await this.messageCollection
  .insertMany(inserts, false)
  .catch((error) => {
  @@ -198,6 +200,7 @@ export class ScribeLambda extends SequencedLambda {
  return Promise.reject(error);
  }
  });
  + }
  // Write out the full state first that we require
  await this.documentCollection.update(
  