Returns
        -------
        Series/Index: object
            The list entries concatenated by intervening occurrences of the
            delimiter.

        Raises
        ------
        AttributeError
            If the supplied Series contains neither strings nor lists.

        See Also
        --------
        str.join : Standard library version of this method.
        Series.str.split : Split strings around given separator/delimiter.

        Notes
        -----
        If any of the list items is not a string object, the result of the join
        will be `NaN`.

        Examples
        --------
        Example with a list that contains non-string elements.

        >>> s = pd.Series([['lion', 'elephant', 'zebra'],
        ...                [1.1, 2.2, 3.3],
        ...                ['cat', np.nan, 'dog'],
        ...                ['cow', 4.5, 'goat'],
        ...                ['duck', ['swan', 'fish'], 'guppy']])
        >>> s
        0        [lion, elephant, zebra]
        1                [1.1, 2.2, 3.3]
        2                [cat, nan, dog]
        3               [cow, 4.5, goat]
        4    [duck, [swan, fish], guppy]
        dtype: object

        Join all lists using a '-'. The lists containing object(s) of types other
        than str will produce a NaN.

        >>> s.str.join('-')
        0    lion-elephant-zebra
        1                    NaN
        2                    NaN
        3                    NaN
        4                    NaN
        dtype: object
        )