* requireNonNull is safe for a properly serialized multimap: We've already inserted a
       * collection for each key that we expect.
       */
      requireNonNull(map.get(key)).add(value);
    }
    setMap(map);
  }

  @GwtIncompatible // java serialization not supported
  @J2ktIncompatible
  private static final long serialVersionUID = 1;

    stream.defaultReadObject();
    expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
    int distinctKeys = Serialization.readCount(stream);
    Map<K, Collection<V>> map = CompactHashMap.create();
    setMap(map);
    Serialization.populateMultimap(this, stream, distinctKeys);
  }

  @GwtIncompatible // Not needed in emulated source.
  @J2ktIncompatible
  private static final long serialVersionUID = 0;

    stream.defaultReadObject();
    keyComparator = requireNonNull((Comparator<? super K>) stream.readObject());
    valueComparator = requireNonNull((Comparator<? super V>) stream.readObject());
    setMap(new TreeMap<K, Collection<V>>(keyComparator));
    Serialization.populateMultimap(this, stream);
  }

  @GwtIncompatible // not needed in emulated source
  @J2ktIncompatible

      stream.defaultReadObject();
      factory = (Supplier<? extends Collection<V>>) requireNonNull(stream.readObject());
      Map<K, Collection<V>> map = (Map<K, Collection<V>>) requireNonNull(stream.readObject());
      setMap(map);
    }

    @GwtIncompatible // java serialization not supported
    @J2ktIncompatible
    private static final long serialVersionUID = 0;
  }

  /**

    stream.defaultReadObject();
    expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
    int distinctKeys = Serialization.readCount(stream);
    Map<K, Collection<V>> map = Maps.newHashMap();
    setMap(map);
    Serialization.populateMultimap(this, stream, distinctKeys);
  }

  @GwtIncompatible // Not needed in emulated source.
  @J2ktIncompatible
  private static final long serialVersionUID = 0;