public IBuilder Append(HrbcField field, FieldCollectionBuilderHandler fieldCollectionHandler)
{
var builder = new CollectionBuilder();
if (content.ContainsKey(field) && content[field] != null)
{
builder.Append(content[field]);
}
fieldCollectionHandler(builder);
content[field] = builder.Count > 0 ? builder.Build() : null;
return(this);
}