camel-cxfrs: NPE on GET request with Content-Type header

This commit  https://github.com/apache/camel/commit/e4ad40f2eebb68cfde175b171538e26b278f63f6 modified DefaultCxfRsBinding.populateCxfRsResponseFromExchange in a way that causes an NPE on line #116 when a GET request is made with the Content-Type header set. Since Camel copies the request headers into the response, this causes the check for Content-Type to find the header and the code after that assumes that cxfExchange.getOutMessage() is non-null.

I can work around this by asking clients not to send the Content-Type header (which is generally meaningless for a GET), but I cannot force them not to send it. I think I can also add header filtering before the endpoint is executed to strip the Content-Type header for GET requests, but ideally DefaultCxfRsBinding.populateCxfRsResponseFromExchange would not call cxfExchange.getOutMessage().putIfAbsent if getOutMessage returns null.