ReactorNettyClientRequest.convertException should include original exception if cause is null

[jhoeller]

one update:

in
your fix

you throw in ReactorNettyClientRequest::convertException - after falling thru - the IOException this way:

return new IOException(ex.getMessage(), cause);

In case of eg. a io.netty.handler.timeout.ReadTimeoutException both are null - the message plus the cause.
So you loose the connex to ex and that it was a timeout that caused the exception.

Consumers like org.springframework.web.client.DefaultRestClient.DefaultRequestBodyUriSpec#createResourceAccessException
don't have this information at hand and throw a ResourceAccessException with "null" message.

Originally posted by @helmut-hackl-dynatrace in #32952 (comment)