private Set<Source> calculateRemovedSources() {
        Set<Source> removed = new HashSet<>();
        for (String src : prev.sources().keySet()) {
            if (now.sources().get(src) == null) {
                removed.add(prev.sources().get(src));
            }
        }
        return removed;
    }
private Set < Source > calculateRemovedSources ( ) { Set < Source > removed = new HashSet < > ( ) ; for ( String src : prev . sources ( ) . keySet ( ) ) { if ( now . sources ( ) . get ( src ) == null ) { removed . add ( prev . sources ( ) . get ( src ) ) ; } } return removed ; }
Return those files belonging to prev, but not now.