preg_replace_callback: Unknown modifier

Problem

I got the following warning this morning: preg_replace_callback(): Unknown modifier 'c'.

This happens in the file advagg/advagg_mod/src/Asset/DeferCss.php on line 72.

    // Put JS inline if configured.
    if ($this->deferMethod === 0) {
      $path = drupal_get_path('module', 'advagg_mod') . '/js/loadCSS.js';
      if (!strpos($content, $path)) {
        $path = Crypt::hashBase64($path . $this->counter);
      }
      $pattern = "/<script src=['\"]\/(.*{$path}.*)\?.*['\"]>/";
      $content = preg_replace_callback($pattern, [$this, 'inlineScript'], $content);
    }

The result is, that $content results in null and the website gets no content (=whitescreen).

Proposed resolution

In my case, the multiple / in the $path breaks the preg_replace_callback. Problem is - in my opinion - that the slashes are not escaped.

I fixed it by adding 2 new lines:

    // Put JS inline if configured.
    if ($this->deferMethod === 0) {
      $path = drupal_get_path('module', 'advagg_mod') . '/js/loadCSS.js';
      if (!strpos($content, $path)) {
        $path = Crypt::hashBase64($path . $this->counter);
+      } else {
+        $path = str_replace('/', '\/', $path);
      }
      $pattern = "/<script src=['\"]\/(.*{$path}.*)\?.*['\"]>/";
      $content = preg_replace_callback($pattern, [$this, 'inlineScript'], $content);
    }

Some details

I am not sure if it's just me with this problem. No problem if it is...
I have enabled these advagg-modules in a rarely empty drupal-project:

• advagg
• advagg_bundler
• advagg_css_minify
• advagg_js_minify
• advagg_mod