At this point he didn't let me add an @Immutable annotation.
A runtime error has come:
java.lang.IllegalStateException: class com.rultor.board.IRCServer$1 is not immutable, can't use it (jcabi-aspects 0.8/22884b9)
	at com.jcabi.aspects.aj.ImmutabilityChecker.after(ImmutabilityChecker.java:73)
	at com.rultor.board.IRCServer$AbstractListener.<init>(IRCServer.java:198)