code: public void removeListener( IDmListener listener ) {
  
  		if( listener != null ) {
  			synchronized( this.dmListeners ) {
  				this.dmListeners.remove( listener );
  			}
  
  			this.logger.info( "The listener '" + listener.getId() + "' is not available anymore in Roboconf's DM." );
  		} else {
  			this.logger.info( "An invalid DM listener was removed." );
  		}
  
  		listListeners();
  	}
docs: Removes a listener.
  @param listener