Laura Dern's starred in stories of marital disaster before - from her portrayal of a no-holds-barreddivorce lawyer in Marriage Story to her turn as a woman on the brink of a marriage breakdown in Big Little Lies. But her new film, Is This Thing On? (out Dec. 19), offers a brighter take on splitsville. Directed and co-written by Bradley Cooper, the movie follows Tess (Dern) and Alex (Will Arnett, also the film's co-writer), parents navigating the beginning of a separation.