private function addNew(string $key, $value): self
    {
        $this->props[$key] = $value;
        return $this;
    }
private function addNew(string $key, $value): self
    {
        $this->props[$key] = $value;
        return $this;
    }
private function addNew ( string $ key , $ value ) : self { $ this -> props [ $ key ] = $ value ; return $ this ; }
addNew item on props

@param mixed $value
addNew item on props