when starting jenkins for the first time (or before the config was saved for the first time)
then startup messages end with an exception when initializing the mdns service.

01.04.2012 19:29:45 hudson.DNSMultiCast <init>
WARNUNG: Failed to advertise the service to DNS multi-cast
java.net.MalformedURLException
at java.net.URL.<init>(URL.java:601)
at java.net.URL.<init>(URL.java:464)
at java.net.URL.<init>(URL.java:413)
at hudson.DNSMultiCast.<init>(DNSMultiCast.java:45)
at jenkins.model.Jenkins.<init>(Jenkins.java:787)
at hudson.model.Hudson.<init>(Hudson.java:81)
at hudson.model.Hudson.<init>(Hudson.java:77)
at hudson.WebAppMain$2.run(WebAppMain.java:217)

this is in fact a null pointer exception, since rootURL is null when the corresponding config file doesn't exist (Mailer config rootURL) if the files haven't been created yet.

This should check for null and simply disable the mdns server I think.