private void emit(SourceRecord inRecord, RowData physicalRow, Collector<RowData> collector) {
        if (!hasMetadata) {
            collector.collect(physicalRow);
            return;
        }

        appendMetadataCollector.inputRecord = inRecord;
        appendMetadataCollector.outputCollector = collector;
        appendMetadataCollector.collect(physicalRow);
    }
A wrapped output collector which is used to append metadata columns after physical columns.
inlong-sort/sort-flink/sort-flink-v1.15/sort-connectors/mongodb-cdc/src/main/java/org/apache/inlong/sort/mongodb/MongoDBConnectorDeserializationSchema.java