text: from .missing_element_base import MissingElementBase
  
  class MissingValueElementBase(MissingElementBase):
      def optional_string_value(self):
          return None
  
      def optional_value(self, _loader):
          return None
  
      def required_string_value(self):
          self._parent._missing_error(self)
  
      def required_value(self, _loader):
          self._parent._missing_error(self)
  