_addSelectionValueObserver() {
		const selection = get( this, "selection" );
		if ( !selection ) { return; }

		const optionValuePath = get( this, "optionValuePath" );
		const selectionValueObserver = () => {
			const value = get( selection, optionValuePath );
			set( this, "value", value );
		};

		this._selection = selection;
		this._selectionValuePath = optionValuePath;
		this._selectionValueObserver = selectionValueObserver;

		addObserver(
			selection,
			optionValuePath,
			selection,
			selectionValueObserver
		);

		this._selectionValueObserver();
	}
Add new selection value observer and execute it to update value attribute