Javadoc generating doesn't work under java8

The default java8 doc generation checks the javadoc for wellformess, all html tags should have a start and end tag. See http://blog.joda.org/2014/02/turning-off-doclint-in-jdk-8-javadoc.html for discussion.

As this has not been a requirement before the javadoc contains a lot of html tags not adhering to this new html4 constraint.