Implements http://jira.sonarsource.com/browse/RSPEC-1186 and replaces http://jira.sonarsource.com/browse/RSPEC-466
Rule "Methods should not be empty" should also detect methods returning only null value
And due to this last change, the PMD rule EmptyMethodInAbstractClassShouldBeAbstract is not replaced anymore by the SonarQube rule S1186.
Manually tested !
Null pointer exception on empty methods contained within enums.