org.activiti.engine.impl.bpmn.behavior.UserTaskActivityBehavior.handleAssignments(UserTaskActivityBehavior.java:132)
org.activiti.engine.impl.bpmn.behavior.UserTaskActivityBehavior.execute(UserTaskActivityBehavior.java:89)
org.activiti.engine.impl.pvm.runtime.AtomicOperationActivityExecute.execute(AtomicOperationActivityExecute.java:45)
org.activiti.engine.impl.interceptor.CommandContext.performOperation(CommandContext.java:88)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:532)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperation(ExecutionEntity.java:527)
org.activiti.engine.impl.pvm.runtime.AtomicOperationTransitionNotifyListenerStart.eventNotificationsCompleted(AtomicOperationTransitionNotifyListenerStart.java:52)
org.activiti.engine.impl.pvm.runtime.AbstractEventAtomicOperation.execute(AbstractEventAtomicOperation.java:56)
org.activiti.engine.impl.interceptor.CommandContext.performOperation(CommandContext.java:88)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:532)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperation(ExecutionEntity.java:527)
org.activiti.engine.impl.pvm.runtime.AbstractEventAtomicOperation.execute(AbstractEventAtomicOperation.java:49)
org.activiti.engine.impl.interceptor.CommandContext.performOperation(CommandContext.java:88)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:532)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperation(ExecutionEntity.java:527)
org.activiti.engine.impl.pvm.runtime.AtomicOperationTransitionCreateScope.execute(AtomicOperationTransitionCreateScope.java:49)
org.activiti.engine.impl.interceptor.CommandContext.performOperation(CommandContext.java:88)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:532)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperation(ExecutionEntity.java:527)
org.activiti.engine.impl.pvm.runtime.AtomicOperationTransitionNotifyListenerTake.execute(AtomicOperationTransitionNotifyListenerTake.java:66)
org.activiti.engine.impl.interceptor.CommandContext.performOperation(CommandContext.java:88)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:532)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperation(ExecutionEntity.java:527)
org.activiti.engine.impl.pvm.runtime.AtomicOperationTransitionDestroyScope.execute(AtomicOperationTransitionDestroyScope.java:116)
org.activiti.engine.impl.interceptor.CommandContext.performOperation(CommandContext.java:88)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:532)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperation(ExecutionEntity.java:527)
org.activiti.engine.impl.pvm.runtime.AtomicOperationTransitionNotifyListenerEnd.eventNotificationsCompleted(AtomicOperationTransitionNotifyListenerEnd.java:36)
org.activiti.engine.impl.pvm.runtime.AbstractEventAtomicOperation.execute(AbstractEventAtomicOperation.java:56)
org.activiti.engine.impl.interceptor.CommandContext.performOperation(CommandContext.java:88)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:532)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperation(ExecutionEntity.java:527)
org.activiti.engine.impl.pvm.runtime.AbstractEventAtomicOperation.execute(AbstractEventAtomicOperation.java:49)
org.activiti.engine.impl.interceptor.CommandContext.performOperation(CommandContext.java:88)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:532)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperation(ExecutionEntity.java:527)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.take(ExecutionEntity.java:367)
org.activiti.engine.impl.bpmn.behavior.BpmnActivityBehavior.performOutgoingBehavior(BpmnActivityBehavior.java:105)
org.activiti.engine.impl.bpmn.behavior.BpmnActivityBehavior.performDefaultOutgoingBehavior(BpmnActivityBehavior.java:54)
org.activiti.engine.impl.bpmn.behavior.FlowNodeActivityBehavior.leave(FlowNodeActivityBehavior.java:44)
org.activiti.engine.impl.bpmn.behavior.FlowNodeActivityBehavior.execute(FlowNodeActivityBehavior.java:36)
org.activiti.engine.impl.pvm.runtime.AtomicOperationActivityExecute.execute(AtomicOperationActivityExecute.java:45)
org.activiti.engine.impl.interceptor.CommandContext.performOperation(CommandContext.java:88)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:532)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperation(ExecutionEntity.java:527)
org.activiti.engine.impl.pvm.runtime.AtomicOperationProcessStartInitial.eventNotificationsCompleted(AtomicOperationProcessStartInitial.java:46)
org.activiti.engine.impl.pvm.runtime.AbstractEventAtomicOperation.execute(AbstractEventAtomicOperation.java:56)
org.activiti.engine.impl.interceptor.CommandContext.performOperation(CommandContext.java:88)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:532)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperation(ExecutionEntity.java:527)
org.activiti.engine.impl.pvm.runtime.AtomicOperationProcessStart.eventNotificationsCompleted(AtomicOperationProcessStart.java:45)
org.activiti.engine.impl.pvm.runtime.AbstractEventAtomicOperation.execute(AbstractEventAtomicOperation.java:56)
org.activiti.engine.impl.interceptor.CommandContext.performOperation(CommandContext.java:88)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:532)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperation(ExecutionEntity.java:527)
org.activiti.engine.impl.persistence.entity.ExecutionEntity.start(ExecutionEntity.java:322)
org.activiti.engine.impl.cmd.StartProcessInstanceCmd.execute(StartProcessInstanceCmd.java:83)
org.activiti.engine.impl.cmd.StartProcessInstanceCmd.execute(StartProcessInstanceCmd.java:36)
org.activiti.engine.impl.interceptor.CommandInvoker.execute(CommandInvoker.java:24)
org.activiti.engine.impl.interceptor.CommandContextInterceptor.execute(CommandContextInterceptor.java:57)
org.activiti.spring.SpringTransactionInterceptor$1.doInTransaction(SpringTransactionInterceptor.java:47)
org.springframework.transaction.support.TransactionTemplate.execute(TransactionTemplate.java:130)
org.activiti.spring.SpringTransactionInterceptor.execute(SpringTransactionInterceptor.java:45)
org.activiti.engine.impl.interceptor.LogInterceptor.execute(LogInterceptor.java:31)
org.activiti.engine.impl.cfg.CommandExecutorImpl.execute(CommandExecutorImpl.java:40)
org.activiti.engine.impl.cfg.CommandExecutorImpl.execute(CommandExecutorImpl.java:35)
org.activiti.engine.impl.RuntimeServiceImpl.startProcessInstanceByKey(RuntimeServiceImpl.java:68)
process.dao.ActivitiDao.doStart(ActivitiDao.java:50)
process.action.util.ActivitiBaseAction.doStart(ActivitiBaseAction.java:52)
process.action.EngineeringPayAction.startProcess(EngineeringPayAction.java:141)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:606)
com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:450)
com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:289)
当我启动一个流程的时候发现这个错误，百思不得其解，重头到尾都检查一遍..
很扯蛋的在数据库找到了原因.一下的对应数据库字段竟然是空的！
