some wrong with upload

view file

PHP Code:

<form method="post" action="" enctype="multipart/form-data">
<input type="file" name="f1">
<input type="submit" name="submit">
</form> 


Controllers file

PHP Code:

    public function upload()
    {
        if($_POST){
            $file = $this->request->getFile('f1');
            $newName = $file->getRandomName();
            if ($file->isValid() && ! $file->hasMoved()){
                $file->move(WRITEPATH.'uploads', $newName);
            }
        }
        echo view('upload');

} 


I got the error

Code:

Method CodeIgniter\HTTP\Header::__toString() must not throw an exception, caught ErrorException: Array to string conversion

May I know where the wrong is? thanks

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