protected void ModifyMetadataCore(PutMappingDescriptor <TType> descriptor)
        {
            var additionalMetadata = ModifyMetadata();

            descriptor.Meta(m =>
            {
                foreach (var metadata in CoreMetadata.Union(additionalMetadata))
                {
                    m.Add(metadata.Key, metadata.Value);
                }
                return(m);
            });
        }