code: public Tuple get(RowKey key) {
  		AssociationOperation result = currentState.get( key );
  		if ( result == null ) {
  			return cleared ? null : snapshot.get( key );
  		}
  		else if ( result.getType() == REMOVE ) {
  			return null;
  		}
  		return result.getValue();
  	}
docs: Returns the association row with the given key.
  
  @param key the key of the row to return.
  @return the association row with the given key or {@code null} if no row with that key is contained in this
  association