validateForm() method is not implemented

validateForm() method is not implemented which allows to load any kind of file to parse. Here is example, the most simplistic implementation which allows you to improve security of this module:

public function validateForm(array &$form, FormStateInterface $form_state) {
$this->file = file_save_upload('csv_file', $form['csv']['csv_file']['#upload_validators'], FALSE, 0);

if (!$this->file) {
$form_state->setErrorByName('csv_file', $this->t('Provided file is not a CSV file or is corrupted.'));
}
}

IMHO module should be avoided until it is fixed as module introduces high security risk.