class Protobuf::Message

def each_field_for_serialization
  all_fields.each do |field|
    next unless __field_must_be_serialized__?(field)
    value = @values[field.name]
    if value.nil?
      # Only way you can get here is if you are required and nil
      raise ::Protobuf::SerializationError, "#{field.name} is required on #{field.message_class}"
    else
      yield(field, value)
    end
  end
end