Beautiful song by Oscar Hammerstein II and Jerome Kern from 1939 (which was a great year for songs: Over the Rainbow, this one, Gone with the Wind, etc.) I'd call this song through composed (several themes and not really a bridge or if it has a bridge it's very short). But no one cares about the form, beautiful melody and of course great lyrics by the Master. (Oscar's grandfather was a big empresario in NY back in the day).