def join_string(part1, part2, concatenation_string = 'AND', seperator=' '):
    """
    Join two strings together using a concatenation string

    Handles the case where either part1 or part2 are an empty string

    @param part1: First string
    @param part2: Second string
    @param concatenation_string: String used to join part1 and part2
    @param seperator: Seperator used to between each part and the
                      concatenation string

    @return A single string that consists of the part1 and part2
            joined together using a concatenation string
    """

    if part1 == '':
        return part2

    elif part2 == '':
        return part1


    if part1[-1] == seperator:
        sep1 = ''
    else:
        sep1 = seperator


    if part2[0] == seperator:
        sep2 = ''
    else:
        sep2 = ' '


    return part1 + sep1 + concatenation_string + sep2 + part2