Prior to this commit, returning an empty mono from an exception handler
registered through ResponseSpec::onStatus would result in memory leaks
(since the response was not read) and in an empty response from bodyTo*
methods of the webclient.
As of this commit, that same empty mono is now interpreted to return
the body (and not an exception), offering a way to override the default
status handlers and return a normal response for 4xx and 5xx status
codes.
a9b3d95a14