@Override
  public boolean canMerge(NumDistinctValueEstimator o) {
    return o instanceof FMSketch && this.numBitVectors == ((FMSketch) o).numBitVectors;
  }
Resets a distinctValueEstimator object to its original state.
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/common/ndv/fm/FMSketch.java