Is it normal that a ConnectionException does not have a message-text??
Is null generally allowed for the message?

Using OpenJDK17 and OpenJDK11.

try
{
    HttpRequest httpreq = HttpRequest.newBuilder ().uri (URI.create ("http://blabla.blabla.blabla")).build ();
    HttpClient httpclnt = HttpClient.newBuilder ().build ();
    HttpResponse <String> httpresp = httpclnt.send (httpreq, HttpResponse.BodyHandlers.ofString ());
}
catch (Exception e)
{
    System.out.println ("EXCEPTION: " + e + "   -    " + e.getMessage ());
}          

Output is

EXCEPTION: java.net.ConnectException   -    null