code: static <K, V> Set<Entry<K, V>> unmodifiableEntrySet(Set<Entry<K, V>> entrySet) {
      return new UnmodifiableEntrySet<>(Collections.unmodifiableSet(entrySet));
    }
docs: Returns an unmodifiable view of the specified set of entries. The {@link Entry#setValue}
  operation throws an {@link UnsupportedOperationException}, as do any operations that would
  modify the returned set.
  
  @param entrySet the entries for which to return an unmodifiable view
  @return an unmodifiable view of the entries