def add_unique_element(self, location, element):
return self._create_entry(location, element, unique=True)<EOL>
Create an entry located at ``location``.

Args:
    location: String or :class:`LocationDescriptor` to describe a "separator location" (i.e. dir1/dir2/dir3 for
        instance).
    element: Element to store.

Returns:
    The created node with the element.

Notes:
    The different sub locations entries **must** exist and the last one **MUST NOT** already exist.
    Use the more loose :meth:`add_element` method if needed.