protected function add_handler( $dependency ) {
		if ( $this->hasConfigKey( $dependency ) ) {
			$handler = $this->hasConfigKey( self::KEY_HANDLERS, $dependency )
				? $this->getConfigKey( self::KEY_HANDLERS, $dependency )
				: $this->get_default_handler( $dependency );
			if ( $handler ) {
				$this->handlers[ $dependency ] = new $handler;
			}
		}
	}