public int getFirstEmpty() {
        int ret = this.inventory.firstEmpty();
        if (ret < 0) {
            throw new IndexOutOfBoundsException("no empty slots");
        }
        return ret;
    }
Gets the initial title which was set when this GUI was made

@return the initial title used when this GUI was made
helper/src/main/java/me/lucko/helper/menu/Gui.java