@Nullable
    @Override
    public String nextSplit() {
        // move the split one (from current value to null)
        final String nextSplit = this.splitId;
        this.splitId = null;

        // move the iterator, from null to value (if first move) or to null (if second move)
        this.recordsForCurrentSplit = nextSplit != null ? this.recordsForSplit : null;
        return nextSplit;
    }
An implementation of {@link RecordsWithSplitIds} which contains the records of one table split.
Copy from com.ververica:flink-cdc-base:2.3.0.
inlong-sort/sort-flink/cdc-base/src/main/java/org/apache/inlong/sort/cdc/base/source/meta/split/ChangeEventRecords.java