MultipartRequestFilter#fileCountMax restricts not only files but any param

Steps to reproduce

1.  Go to demo and edit the MultipartRequestFilter at [servers/filter|/server/filters/multipartRequest] section
2.  Include a new attribute named fileCountMax and set its value to 1
3. Include a new attribute named maxFileSize and set its value to 2000000000
4. Go to travel/members/registration form
5. Fulfill the form and send it
6. Check a 500 Internal error is thrown

Expected results

The form is sent and processed without issues as far as it has no files (only fields)

Actual results

500 Internal server error is thrown

Workaround

Increase fileCountMax https://docs.magnolia-cms.com/product-docs/6.2/Administration/Architecture/Request-processing-and-filters/Filters.html#_multipart_request

Development notes

Attached the log stack trace