@Nullable
    public BsonDocument getResumeToken() {
        String resumeTokenJson = offset.get(RESUME_TOKEN_FIELD);
        return Optional.ofNullable(resumeTokenJson).map(BsonDocument::parse).orElse(null);
    }
A structure describes a fine grained offset in a change log event including resumeToken and
clusterTime.
Copy from com.ververica:flink-connector-mongodb-cdc:2.3.0.
inlong-sort/sort-flink/sort-flink-v1.13/sort-connectors/mongodb-cdc/src/main/java/org/apache/inlong/sort/cdc/mongodb/source/offset/ChangeStreamOffset.java