CLONE - Content length missing in HTTP header

We are using org.apache.cxf.jaxrs.client.WebClient in our solution where we send a list of custom headers. 

All but "Content-Length" are included and sent. We also tried to disable chunking, but it had no effect.

Issue exist in org.apache.cxf:cxf-rt-rs-client package, both 3.3.4 and 3.3.5 versions. We are using Java 8 mainly. We also tried with Java 13 with no success.

Partial code:

Map<String, Object> headers;

...

...

...
Client client = WebClient.client(api);
if (headers != null)
    headers.forEach(client::header);

We've managed to debug this and found out that all the headers are kept in the "PROTOCOL_HEADERS" map up until the actual request is made. At that point, "Content-Length" is omitted. 

On a side note, body is "null" for the request. Shouldn't the "Content-Length : 0" be automatically added?