Willie Nelson made a guest appearance during The Muppets season finale on Tuesday night to perform one of his classic songs, “On the Road Again.”  On the show, Nelson performs the tune, released in 1980, for Miss Piggy while she is in the hospital. A crew of the Muppets — together known as Electric Mayhem — join the country icon for the song, playing additional instruments and adding harmonies as Miss Piggy, Kermit and some doctors and fellow patients look on. MORE…