Error message when e-mail is sent

The drupal 8 version of the module works great and the outgoing e-mails are HTML formatted, but when the system sends the e-mail, an error message appers:

Strict warning: Non-static method Drupal\mimemail\Utility\MimeMailFormatHelper::replaceFiles() should not be called statically in Drupal\mimemail\Utility\MimeMailFormatHelper::mimeMailExtractFiles() (line 182 of modules/contrib/mimemail/src/Utility/MimeMailFormatHelper.php).

I updated the code in the modules/contrib/mimemail/src/Utility/MimeMailFormatHelper.php file (line number: 578) and the error message is gone.

I replaced this:
public function replaceFiles($matches) {

with this:
public static function replaceFiles($matches) {