Serialize the value and append it to the parent element.

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)