* and values are the result of applying the provided mapping functions to the input elements.
   * Entries appear in the result {@code ImmutableBiMap} in encounter order.
   *
   * <p>If the mapped keys or values contain duplicates (according to {@link
   * Object#equals(Object)}), an {@code IllegalArgumentException} is thrown when the collection

   *
   * <p>When there are multiple instances of a key in this iterable, it is unspecified whether
   * {@code valueFunction} will be applied to more than one instance of that key and, if it is,
   * which result will be mapped to that key in the returned map.
   *
   * <p><b>{@code Stream} equivalent:</b> use {@code stream.collect(ImmutableMap.toImmutableMap(k ->