@Override
  public synchronized Object compute(Object key, BiFunction remappingFunction) {
    if (interned != null) copyFromInternedToThis();  // We do this because if function returns null,
                                       // the mapping for key is removed, i.e. the table is mutated.
    return super.compute(key, remappingFunction);
  }
**********   Public API of java.util.Hashtable   ***********
common/src/java/org/apache/hadoop/hive/common/CopyOnFirstWriteProperties.java