Better validation exceptions

badwitch.py

@@ -47,11 +47,9 @@ class Library:
         try:
             for album, albumcontent in self.albums.items():
                 for song, songcontent in albumcontent.items():
-                    if songcontent['artist'] is None:
-                        raise Exception
-        except:
-            logging.warn('Library not valid')
-            raise Exception('Library not valid')
+                    for field in ['track', 'artist', 'source']:
+                        if field not in songcontent:
+                            raise Exception('Song is missing required field', song, field)
 
     # Download library
     def download(self, targetalbum=None):