docs: public static <K, V> Map<K, V> copyMapButFailOnNull(Map<? extends K, ? extends V> entries) {
      Map<K, V> entriesToRemap = new HashMap<>(entries.size());
      entries.forEach((k, v) -> {
        // If a key/value is null, throw NPE, nothing gets mutated
        if (k == null || v == null) {
          throw new NullPointerException();
        }
        entriesToRemap.put(k, v);
      });
      return entriesToRemap;
    }