docs: def serialize(
              self,
              value,  # type: Any
              state  # type: _ProcessorState
      ):
          # type: (...) -> ET.Element
          """Serialize the value into a new Element object and return it."""
          if self._nested is None:
              state.raise_error(InvalidRootProcessor,
                                'Cannot directly serialize a non-nested array "{}"'
                                .format(self.alias))
  
          if not value and self.required:
              state.raise_error(MissingValue, 'Missing required array: "{}"'.format(
                  self.alias))
  
          start_element, end_element = _element_path_create_new(self._nested)
          self._serialize(end_element, value, state)
  
          return start_element