code: private ChangeEvent<BsonDocument> getSynthesizedRemoteChangeEventForDocument(
        final MongoNamespace ns,
        final BsonValue documentId,
        final BsonDocument document
    ) {
      // a. When the document is looked up, if it cannot be found the synthesized change event is a
      // DELETE, otherwise it's a REPLACE.
      if (document == null) {
        return ChangeEvents.changeEventForLocalDelete(ns, documentId, false);
      }
      return ChangeEvents.changeEventForLocalReplace(ns, documentId, document, false);
    }
docs: Returns a synthesized change event for a remote document.
  
  @param ns         the namspace where the document lives.
  @param documentId the _id of the document.
  @param document   the remote document.
  @return a synthesized change event for a remote document.