public function store($label)
    {
        if ($this->icon === null) {
            throw new CollectionIconException(
                'There was no icon defined to store.'
            );
        }

        if (is_string($label) === false || empty($label) === true) {
            throw new \InvalidArgumentException(
                'Collection icon label must be a non-empty string.'
            );
        }

        $this->collection[$label] = $this->output();

        return $this;
    }