!16 修复了当流程发起者的部门为空时，打开已办任务报错的问题

Merge pull request !16 from undefined/master

ruoyi-flowable/src/main/java/com/ruoyi/flowable/service/impl/FlowTaskServiceImpl.java

@@ -786,7 +786,9 @@ public class FlowTaskServiceImpl extends FlowServiceFactory implements IFlowTask
             SysUser startUser = sysUserService.selectUserById(Long.parseLong(historicProcessInstance.getStartUserId()));
             flowTask.setStartUserId(startUser.getNickName());
             flowTask.setStartUserName(startUser.getNickName());
+            if(Objects.nonNull(startUser.getDept())) {
                 flowTask.setStartDeptName(startUser.getDept().getDeptName());
+            }
             hisTaskList.add(flowTask);
         }
         page.setTotal(taskInstanceQuery.count());