class Protobuf::Message

def each_field_for_serialization
  self.class.all_fields.each do |field|
    next unless field_must_be_serialized?(field)
    value = @values[field.getter]
    if value.nil?
      raise ::Protobuf::SerializationError, "Required field #{self.class.name}##{field.name} does not have a value."
    else
      yield(field, value)
    end
  end
end