code: def to_lower(cls):  # NOQA
          
  
          email = cls.get_fields_by_class(EmailType)
          lower = cls.get_fields_by_prop('lower', True) + email
  
          return list(set(email + lower))
docs: Return a list of all the fields that should be lowercased
  
          This is done on fields with `lower=True`.