code: public boolean validate(DependencyExplorerOutput output, InvalidKeys invalidKeys) {
      Collection<Map.Entry<Key<?>, String>> invalidRequiredKeys = 
          invalidKeys.getInvalidRequiredKeys();
      for (Map.Entry<Key<?>, String> error : invalidRequiredKeys) {
        reportError(output, error.getKey(), error.getValue());
      }
      
      return !cycleFinder.findAndReportCycles(output.getGraph()) && invalidRequiredKeys.isEmpty();
    }
docs: Returns true if the graph is valid (does not have any cycles or problems creating required
  keys).  If there are any errors, they will be reported to the global {@link ErrorManager}.