@Override
  public TypeV   remove     ( Object key )            { return putIfMatch( key,TOMBSTONE, NO_MATCH_OLD); }
Removes the key (and its corresponding value) from this map.
 This method does nothing if the key is not in the map.
 @return the previous value associated with <tt>key</tt>, or
        <tt>null</tt> if there was no mapping for <tt>key</tt>
 @throws NullPointerException if the specified key is null
jctools-core/src/main/java/org/jctools/maps/NonBlockingIdentityHashMap.java