public ImmutableMap <TKey, TValue> AddRange([NotNull] IEnumerable <KeyValuePair <TKey, TValue> > pairs)
{
if (pairs is null)
{
throw new ArgumentNullException(nameof(pairs));
}
pairs = pairs.Materialize();
return(new ImmutableMap <TKey, TValue>(Base.AddRange(pairs), Reversed.AddRange(pairs.ReversePairs())));
}