code: private static @Nullable Collection<IOException> concat(
        @Nullable Collection<IOException> exceptions, @Nullable Collection<IOException> other) {
      if (exceptions == null) {
        return other;
      } else if (other != null) {
        exceptions.addAll(other);
      }
      return exceptions;
    }
docs: Concatenates the contents of the two given collections of exceptions. If either collection is
  null, the other collection is returned. Otherwise, the elements of {@code other} are added to
  {@code exceptions} and {@code exceptions} is returned.