There are multiple non-interrupt scheduled task boundary events on the user task that are executed concurrently and an error occurs. How should I solve this problem?

[xingwenkai]

19:15:24.627 [task-20] ERROR o.a.e.i.i.CommandContext - [logException,149] - Error while closing command context
java.lang.NullPointerException: null
at org.activiti.engine.impl.persistence.entity.JobEntityManagerImpl.delete(JobEntityManagerImpl.java:158)
at org.activiti.engine.impl.persistence.entity.JobEntityManagerImpl.delete(JobEntityManagerImpl.java:30)
at org.activiti.engine.impl.persistence.entity.AbstractEntityManager.delete(AbstractEntityManager.java:87)
at org.activiti.engine.impl.persistence.entity.JobEntityManagerImpl.delete(JobEntityManagerImpl.java:142)
at org.activiti.engine.impl.persistence.entity.JobEntityManagerImpl.delete(JobEntityManagerImpl.java:30)
at org.activiti.engine.impl.persistence.entity.AbstractEntityManager.delete(AbstractEntityManager.java:82)
at org.activiti.engine.impl.asyncexecutor.DefaultJobManager.unacquire(DefaultJobManager.java:230)
at org.activiti.engine.impl.asyncexecutor.ExecuteAsyncRunnable$2.execute(ExecuteAsyncRunnable.java:149)
at org.activiti.engine.impl.asyncexecutor.ExecuteAsyncRunnable$2.execute(ExecuteAsyncRunnable.java:147)
at org.activiti.engine.impl.interceptor.CommandInvoker$1.run(CommandInvoker.java:37)
at org.activiti.engine.impl.interceptor.CommandInvoker.executeOperation(CommandInvoker.java:78)
at org.activiti.engine.impl.interceptor.CommandInvoker.executeOperations(CommandInvoker.java:57)
at org.activiti.engine.impl.interceptor.CommandInvoker.execute(CommandInvoker.java:42)
at org.activiti.engine.impl.interceptor.TransactionContextInterceptor.execute(TransactionContextInterceptor.java:48)
at org.activiti.engine.impl.interceptor.CommandContextInterceptor.execute(CommandContextInterceptor.java:59)
at org.activiti.spring.SpringTransactionInterceptor$1.doInTransaction(SpringTransactionInterceptor.java:47)
at org.springframework.transaction.support.TransactionTemplate.execute(TransactionTemplate.java:140)
at org.activiti.spring.SpringTransactionInterceptor.execute(SpringTransactionInterceptor.java:45)
at org.activiti.engine.impl.interceptor.LogInterceptor.execute(LogInterceptor.java:29)
at org.activiti.engine.impl.cfg.CommandExecutorImpl.execute(CommandExecutorImpl.java:44)
at org.activiti.engine.impl.cfg.CommandExecutorImpl.execute(CommandExecutorImpl.java:39)
at org.activiti.engine.impl.asyncexecutor.ExecuteAsyncRunnable.unacquireJob(ExecuteAsyncRunnable.java:147)
at org.activiti.engine.impl.asyncexecutor.ExecuteAsyncRunnable.lockJobIfNeeded(ExecuteAsyncRunnable.java:134)
at org.activiti.engine.impl.asyncexecutor.ExecuteAsyncRunnable.run(ExecuteAsyncRunnable.java:66)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Exception in thread "task-20" java.lang.NullPointerException
at org.activiti.engine.impl.persistence.entity.JobEntityManagerImpl.delete(JobEntityManagerImpl.java:158)
at org.activiti.engine.impl.persistence.entity.JobEntityManagerImpl.delete(JobEntityManagerImpl.java:30)
at org.activiti.engine.impl.persistence.entity.AbstractEntityManager.delete(AbstractEntityManager.java:87)
at org.activiti.engine.impl.persistence.entity.JobEntityManagerImpl.delete(JobEntityManagerImpl.java:142)
at org.activiti.engine.impl.persistence.entity.JobEntityManagerImpl.delete(JobEntityManagerImpl.java:30)
at org.activiti.engine.impl.persistence.entity.AbstractEntityManager.delete(AbstractEntityManager.java:82)
at org.activiti.engine.impl.asyncexecutor.DefaultJobManager.unacquire(DefaultJobManager.java:230)
at org.activiti.engine.impl.asyncexecutor.ExecuteAsyncRunnable$2.execute(ExecuteAsyncRunnable.java:149)
at org.activiti.engine.impl.asyncexecutor.ExecuteAsyncRunnable$2.execute(ExecuteAsyncRunnable.java:147)
at org.activiti.engine.impl.interceptor.CommandInvoker$1.run(CommandInvoker.java:37)
at org.activiti.engine.impl.interceptor.CommandInvoker.executeOperation(CommandInvoker.java:78)
at org.activiti.engine.impl.interceptor.CommandInvoker.executeOperations(CommandInvoker.java:57)
at org.activiti.engine.impl.interceptor.CommandInvoker.execute(CommandInvoker.java:42)
at org.activiti.engine.impl.interceptor.TransactionContextInterceptor.execute(TransactionContextInterceptor.java:48)
at org.activiti.engine.impl.interceptor.CommandContextInterceptor.execute(CommandContextInterceptor.java:59)
at org.activiti.spring.SpringTransactionInterceptor$1.doInTransaction(SpringTransactionInterceptor.java:47)
at org.springframework.transaction.support.TransactionTemplate.execute(TransactionTemplate.java:140)
at org.activiti.spring.SpringTransactionInterceptor.execute(SpringTransactionInterceptor.java:45)
at org.activiti.engine.impl.interceptor.LogInterceptor.execute(LogInterceptor.java:29)
at org.activiti.engine.impl.cfg.CommandExecutorImpl.execute(CommandExecutorImpl.java:44)
at org.activiti.engine.impl.cfg.CommandExecutorImpl.execute(CommandExecutorImpl.java:39)
at org.activiti.engine.impl.asyncexecutor.ExecuteAsyncRunnable.unacquireJob(ExecuteAsyncRunnable.java:147)
at org.activiti.engine.impl.asyncexecutor.ExecuteAsyncRunnable.lockJobIfNeeded(ExecuteAsyncRunnable.java:134)
at org.activiti.engine.impl.asyncexecutor.ExecuteAsyncRunnable.run(ExecuteAsyncRunnable.java:66)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)