No content-length header after upgrade CXF from 3.5.6 to 3.6.1

After updating the CXF dependency in our application from 3.5.6 to 3.6.1 it does not add a content-length header anymore, when doing a multipart request for a file upload.

I didn't find any information, how to let CXF set the header. Is it just dependent of chunking?

Actually the application sets "allow chunking" to false. But I'm not sure, how I can test, if this really works.

Thanks in advance for your help.