处理合奏时没有声部的空指针异常

cooleshow-user/user-biz/src/main/java/com/yonge/cooleshow/biz/dal/service/impl/MusicSheetServiceImpl.java

@@ -868,7 +868,8 @@ public class MusicSheetServiceImpl extends ServiceImpl<MusicSheetDao, MusicSheet
         }*/
 
         // 删除曲目专辑关联
-        if (oldMusicSheet != null && !oldMusicSheet.getMusicSubject().equals(musicSheetDto.getMusicSubject())) {
+        if (oldMusicSheet != null && oldMusicSheet.getMusicSubject() != null
+                && !oldMusicSheet.getMusicSubject().equals(musicSheetDto.getMusicSubject())) {
             delAlbumSheetRef(musicSheetDto.getId(), musicSheetDto.getMusicSubject());
         }