当我运行activiti项目时，出现了问题。这是错误日志
java.lang.NullPointerException
at org.activiti.engine.impl.pvm.process.ScopeImpl.contains(ScopeImpl.java:76)
at org.activiti.engine.impl.pvm.runtime.AtomicOperationTransitionDestroyScope.transitionLeavesNextOuterScope(AtomicOperationTransitionD
estroyScope.java:121)
at org.activiti.engine.impl.pvm.runtime.AtomicOperationTransitionDestroyScope.execute(AtomicOperationTransitionDestroyScope.java:112)
at org.activiti.engine.impl.interceptor.CommandContext.performOperation(CommandContext.java:97)
at org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:650)
at org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperation(ExecutionEntity.java:643)
at org.activiti.engine.impl.pvm.runtime.AtomicOperationTransitionNotifyListenerEnd.eventNotificationsCompleted(AtomicOperationTransitio
nNotifyListenerEnd.java:35)
at org.activiti.engine.impl.pvm.runtime.AbstractEventAtomicOperation.execute(AbstractEventAtomicOperation.java:56)
at org.activiti.engine.impl.interceptor.CommandContext.performOperation(CommandContext.java:97)
at org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:650)
at org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperation(ExecutionEntity.java:643)
at org.activiti.engine.impl.pvm.runtime.AbstractEventAtomicOperation.execute(AbstractEventAtomicOperation.java:49)
at org.activiti.engine.impl.interceptor.CommandContext.performOperation(CommandContext.java:97)
at org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:650)
at org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperation(ExecutionEntity.java:643)
at org.activiti.engine.impl.persistence.entity.ExecutionEntity.take(ExecutionEntity.java:460)
at org.activiti.engine.impl.persistence.entity.ExecutionEntity.take(ExecutionEntity.java:438)
at org.activiti.engine.impl.bpmn.behavior.BpmnActivityBehavior.performOutgoingBehavior(BpmnActivityBehavior.java:140)
at org.activiti.engine.impl.bpmn.behavior.BpmnActivityBehavior.performDefaultOutgoingBehavior(BpmnActivityBehavior.java:66)
at org.activiti.engine.impl.bpmn.behavior.FlowNodeActivityBehavior.leave(FlowNodeActivityBehavior.java:44)
at org.activiti.engine.impl.bpmn.behavior.AbstractBpmnActivityBehavior.leave(AbstractBpmnActivityBehavior.java:47)
at org.activiti.engine.impl.bpmn.behavior.UserTaskActivityBehavior.signal(UserTaskActivityBehavior.java:228)
at org.activiti.engine.impl.persistence.entity.ExecutionEntity.signal(ExecutionEntity.java:417)
at org.activiti.engine.impl.persistence.entity.TaskEntity.complete(TaskEntity.java:203)
at org.activiti.engine.impl.cmd.CompleteTaskCmd.execute(CompleteTaskCmd.java:52)
at org.activiti.engine.impl.cmd.CompleteTaskCmd.execute(CompleteTaskCmd.java:24)
at org.activiti.engine.impl.cmd.NeedsActiveTaskCmd.execute(NeedsActiveTaskCmd.java:59)
at org.activiti.engine.impl.interceptor.CommandInvoker.execute(CommandInvoker.java:24)
at org.activiti.engine.impl.interceptor.CommandContextInterceptor.execute(CommandContextInterceptor.java:57)
at org.activiti.spring.SpringTransactionInterceptor$1.doInTransaction(SpringTransactionInterceptor.java:47)
at org.springframework.transaction.support.TransactionTemplate.execute(TransactionTemplate.java:133)
at org.activiti.spring.SpringTransactionInterceptor.execute(SpringTransactionInterceptor.java:45)
at org.activiti.engine.impl.interceptor.LogInterceptor.execute(LogInterceptor.java:31)
at org.activiti.engine.impl.cfg.CommandExecutorImpl.execute(CommandExecutorImpl.java:40)
at org.activiti.engine.impl.cfg.CommandExecutorImpl.execute(CommandExecutorImpl.java:35)
at org.activiti.engine.impl.TaskServiceImpl.complete(TaskServiceImpl.java:182)