code: def validate_user_email(self, value):
          
          enterprise_customer = self.context.get('enterprise_customer')
  
          try:
              user = User.objects.get(email=value)
              return models.EnterpriseCustomerUser.objects.get(
                  user_id=user.id,
                  enterprise_customer=enterprise_customer
              )
          except (models.EnterpriseCustomerUser.DoesNotExist, User.DoesNotExist):
              pass
  
          return value
docs: Validates the user_email, if given, to see if an existing EnterpriseCustomerUser exists for it.
  
          If it does not, it does not fail validation, unlike for the other field validation methods above.