protected override void Add(ImmutableSortedDictionary <TKey, TValue> .Builder collection, int index, TKey key, TValue value)
 {
     collection.Add(key, value);
 }
 protected void ContainsValueTestHelper <TKey, TValue>(ImmutableSortedDictionary <TKey, TValue> map, TKey key, TValue value)
 {
     Assert.False(map.ContainsValue(value));
     Assert.True(map.Add(key, value).ContainsValue(value));
 }
 protected override void Add(ImmutableSortedDictionary <TKey, TValue> .Builder collection, int index, TKey key, TValue value, MessagePackSerializerOptions options)
 {
     collection.Add(key, value);
 }