IOException is produced when delete-buidls is invoked with a repeated build number.
It can be made by mistake e.g. delete-builds 1,2,3,3 or intentionally e.g. delete-builds 1-6,3-10.
DeleteBuildsCommand class is derived from AbstractBuildRangeCommand where it is possible to have a build specified more times for whatever reason. In current impl. it is responsibility of DeleteBuildsCommand to handle that situation correctly.