[silin]

on (rollOver) {
	if (text_2.text == undefined || text_2.text == '') {
		this.blu._alpha = 0;
	} else {
		this.blu._alpha = 70;
	}
}

или, что тоже самое

on (rollOver) {
	this.blu._alpha = text_2.text ? 70 : 0;
}