Airship\Engine\Lens::append PHP Method

    public function append(string $key, $val) : self
    {
        if (!isset($this->stored[$key])) {
            $this->stored[$key] = [];
        } elseif (!is_array($this->stored[$key])) {
            // Let's store the existing value as the first index
            $this->stored[$key] = [$this->stored[$key]];
        }
        $this->stored[$key][] = $val;
        return $this;
    }