code: public Set<Library> getMissingLibraries(MinecraftDirectory minecraftDir) {
  		Set<Library> missing = new LinkedHashSet<>();
  		for (Library library : libraries)
  			if (library.isMissing(minecraftDir))
  				missing.add(library);
  		return Collections.unmodifiableSet(missing);
  	}
docs: Returns the missing libraries in the given minecraft directory.
  
  @param minecraftDir the minecraft directory to check
  @return true the missing libraries in the given minecraft directory, an
  empty set if no library is missing