upload a file

Hello I need help to know how to updload an image.  I find example but nothing works either it is codeigniter 3 or it does not work for me

I created a form with
  <input type="file" name="acimage" />


On my controller I have ...
      $file = $this->request->getFile('acimage');
      if (! $file->isValid())
        {
                throw new RuntimeException($file->getErrorString().'('.$file->getError().')');
        }


On the line if (! $file->isValid())


I have the same kind of error

Call to a member function isValid() on null

same kind of error with
$file->getName();

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not easy to write simple in black. Sorry

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Is this page

https://makitweb.com/how-to-upload-file-in-codeigniter/

Still valid with codeigniter 4