Headless Server Bugfix: Empty HTML in Html Fragments leads to Exception

When the HTML in a HTML fragment is left empty, a serverside exception was thrown by the HtmlAdapter. The adapter now returns null instead.

(CMS-25610)

Headless server can be run without commerce extension

There was a dependency for the headless server that could be satisfied without the commerce extension. However, this was not intentional and now the required component is also found without having the commerce extension enabled.

(CMS-25435)