code: Set<String> dependences(Archive source) {
          if (!results.containsKey(source)) {
              return Collections.emptySet();
          }
  
          return results.get(source).dependencies()
                        .stream()
                        .map(Dep::target)
                        .collect(Collectors.toSet());
      }
docs: Returns the dependences, either class name or package name
  as specified in the given verbose level, from the given source.