docs: def serialize_on_parent(
              self,
              parent,  # type: ET.Element
              value,  # type: Any
              state  # type: _ProcessorState
      ):
          # type: (...) -> None
          """Serialize the value and append it to the parent element."""
          if not value and self.required:
              state.raise_error(MissingValue, 'Missing required array: "{}"'.format(
                  self.alias))
  
          if not value and self.omit_empty:
              return  # Do nothing
  
          if self._nested is not None:
              array_parent = _element_get_or_add_from_parent(parent, self._nested)
          else:
              # Embedded array has all items serialized directly on the parent.
              array_parent = parent
  
          self._serialize(array_parent, value, state)