put Validation Rules to the Config File

IN CI4,
I put the Validation Rules to the Config File(Validation)

Code:

    // Rules
    public $signup = [
       'username'     => 'required',
       'password'     => 'required',
       'pass_confirm' => 'required|matches[password]',
       'email'        => 'required|valid_email'
   ];

here I test it in Controller:

PHP Code:

            $validation =  \Config\Services::validation();
            $data=array(
                'email'=>'',
                'username'=>'',
            );
            $validation->run($data, $signup);
            $errors = $validation->getErrors();
            print_r($errors); 


I got the ErrorException #1

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

 what went wrong?

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