code: private void addEntries(final FileSystem zipFs) throws IOException {
  
          for (Map.Entry<String, URL> entry : contentMap.entrySet()) {
              final Path pathToFile = zipFs.getPath(entry.getKey());
              final URL resource = entry.getValue();
              addResource(pathToFile, resource);
          }
      }
docs: Adds the entries to the zip file, that have been defined by the builder.
  
  @param zipFs
  the zip file system that represents the new zip file.
  
  @throws IOException