When configuring the IRC plugin of a new Docker Jenkins installation, I've got an uncaught NullPointerException, and the bot doesn't seem to connect on the server

Note: I can use netcat from the container to log in successfully on the server (netcat barjavel.freenode.net 8000), but it doesn't work .

Stacktrace and log

Nov 13, 2015 4:26:41 AM INFO hudson.plugins.ircbot.v2.IRCConnection connect
Connecting to barjavel.freenode.net :8000 as Alken-Orin using charset UTF-8
Nov 13, 2015 4:26:41 AM WARNING hudson.plugins.ircbot.v2.IRCConnection connect
Error connecting to irc
java.lang.NullPointerException
at org.pircbotx.PircBotX.shutdown(PircBotX.java:2853)
at org.pircbotx.PircBotX.connect(PircBotX.java:452)
at hudson.plugins.ircbot.v2.IRCConnection.connect(IRCConnection.java:135)
at hudson.plugins.ircbot.v2.IRCConnectionProvider.createConnection(IRCConnectionProvider.java:37)
at hudson.plugins.im.IMConnectionProvider.create(IMConnectionProvider.java:59)
at hudson.plugins.im.IMConnectionProvider.access$500(IMConnectionProvider.java:16)
at hudson.plugins.im.IMConnectionProvider$ConnectorRunnable.run(IMConnectionProvider.java:165)
at java.lang.Thread.run(Thread.java:745)