code: public V remove( final K key ) {
          synchronized ( _map ) {
              final ManagedItem<V> removed = _map.remove( key );
              return removed != null ? removed._value : null;
          }
      }
docs: Removes the mapping for the specified key from this map if present.
  
  @param  key key whose mapping is to be removed from the map
  @return
  @return the previous value associated with <tt>key</tt>, or
  <tt>null</tt> if there was no mapping for <tt>key</tt>.
  (A <tt>null</tt> return can also indicate that the map
  previously associated <tt>null</tt> with <tt>key</tt>.)