src/Collection.php
private function appendToArray(string $key, $value): self
    {
        $this->props[$key] = [$this->props[$key], $value];

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

        return $this;
    }
private function appendToArray ( string $ key , $ value ) : self { $ this -> props [ $ key ] = [ $ this -> props [ $ key ] , $ value ] ; return $ this ; }
appending to already existing array

@param mixed $value
appending to already existing array