【bug】优化变更字段判断逻辑

mes-module-heli/mes-module-heli-biz/src/main/java/com/chanko/yunxi/mes/module/heli/service/projectorder/ProjectOrderServiceImpl.java

@@ -259,7 +259,7 @@ public class ProjectOrderServiceImpl implements ProjectOrderService {
                     Map<String, List<ProjectOrderSubDO>> nameGroups = lastSnapshotSubDOList.stream().collect(Collectors.groupingBy(ProjectOrderSubDO::getName));
                     projectOrderSubDOList.forEach(projectOrderSubDO -> {
                         List<ProjectOrderSubDO> lastSnapshotSubs = nameGroups.get(projectOrderSubDO.getName());
-                        if(lastSnapshotSubs.isEmpty()) return;
+                        if(lastSnapshotSubs == null || lastSnapshotSubs.isEmpty()) return;
                         List<FieldInfo> diffFields = FIELD_EQUATOR.getDiffFields(projectOrderSubDO, lastSnapshotSubs.get(0));
                         projectOrderSubDO.setAlterFieldNames(diffFields.stream().map(FieldInfo::getFieldName).collect(Collectors.toSet()));
                     });