code: def to_array(self):
          
          array = super(Invoice, self).to_array()
          array['title'] = u(self.title)  # py2: type unicode, py3: type str
          array['description'] = u(self.description)  # py2: type unicode, py3: type str
          array['start_parameter'] = u(self.start_parameter)  # py2: type unicode, py3: type str
          array['currency'] = u(self.currency)  # py2: type unicode, py3: type str
          array['total_amount'] = int(self.total_amount)  # type int
          return array
docs: Serializes this Invoice to a dictionary.
  
          :return: dictionary representation of this object.
          :rtype: dict