docs: def add_new_source(self, source_token, stripe_js_response=None):
          """Add new source (for example: a new card) to the customer
  
          The new source will be automatically set as customer's default payment source.
          Passing stripe_js_response is optional. If set, StripeCustomer.stripe_js_response will be updated.
          """
          customer = self.retrieve_from_stripe()
          customer.source = source_token
          customer.save()
          if stripe_js_response:
              self.stripe_js_response = stripe_js_response
          self._update_from_stripe_object(customer)