fix 合奏班列表显示问题

mec-biz/src/main/java/com/ym/mec/biz/service/impl/ClassGroupServiceImpl.java

@@ -128,7 +128,10 @@ public class ClassGroupServiceImpl extends BaseServiceImpl<Integer, ClassGroup>
     public List<ClassGroup> findAllMixClassGroupByMusicGroupId(String musicGroupId) {
         List<ClassGroup> allMixClassGroup = classGroupDao.findAllMixClassGroup(musicGroupId);
         for (ClassGroup mixClassGroup : allMixClassGroup) {
-            mixClassGroup.setClassNames(classGroupDao.findMixClassChildClassGroupNames(mixClassGroup.getId()).getName());
+            ClassGroup mixClassChildClassGroup = classGroupDao.findMixClassChildClassGroupNames(mixClassGroup.getId());
+            if(mixClassChildClassGroup != null){
+                mixClassGroup.setClassNames(mixClassChildClassGroup.getName());
+            }
         }
         return allMixClassGroup;
     }