code: public static @Nonnull <T> List<T> unmodifiableList(@Nullable List<T> list) {
          if (isEmpty(list)) {
              return Collections.emptyList();
          }
          return Collections.unmodifiableList(list);
      }
docs: Null safe version of {@link Collections#unmodifiableList(List)}.
  
  @param list The list
  @param <T> The generic type
  @return A non-null unmodifiable list