docs: @SuppressWarnings("ConstantConditions")
    private ImmutableMap<K,V> toRegularImmutableMap() {
      final ImmutableMap.Builder<K, V>  ret = ImmutableMap.builder();
  
      for (final MapEntry<K, V> entry : entries) {
        ret.put(entry.key, entry.value);
      }
  
      return ret.build();
    }