Double slash when generating the URL

I have a View Mode Page configured for the "teaser" view mode of a node with a pattern of /teaser/%. I create a node with a URL alias of /test/page. The teaser view mode is accessible via /teaser/test/page. But when I generate the URL, it results in a double slash /teaser//test/page.

$url = new Url(
  'view_mode_page.display_entity',
  [
    'view_mode' => 'teaser',
    'entity_type' => 'node',
    'entity_id' => $node_id,
  ]
);
echo $url->toString(); // results in /teaser//test/page

It seems like a potential issue in \Drupal\view_mode_page\PathProcessor\DynamicPathProcessor::processOutbound where this is called:

$path = str_replace('%', $url_alias, $pattern->getPattern());

When our URL alias = /test/page and our pattern = /teaser/%, then the string replace of % with /test/page would result in /teaser//test/page. Since all aliases begin with a leading slash, should we instead string replace "/%" to account for this?

$path = str_replace('/%', $url_alias, $pattern->getPattern());

This works for my specific use-case? The only scenario it doesn't work for is if your % is not immediately preceded by a slash, but I don't think these paths resolve properly anyway. I'm not sure why the error doesn't present itself with patterns where the % appears at the beginning of the path, like /%/teaser but my fix doesn't break those either.