Activiti表达式报错：Unknown property used in e?报错

public class Leave implements Serializable
{
private static final long serialVersionUID = 1L;
private String name;
private Integer day;
private Integer total = 0;


//省略set,get
}

bpmn里面配置的是：
<conditionExpression xsi:type="tFormalExpression"><![CDATA[${reason[0].total < 10}]]></conditionExpression>

启动流程实例的时候，是这样的

Map<String, Object> vars = new HashMap<>();

processEngine.getRuntimeService().startProcessInstanceByKey("dingcan", vars);

随后，执行报错

org.activiti.engine.ActivitiException: Unknown property used in expression: ${reason[0].total < 10}
	at org.activiti.engine.impl.el.JuelExpression.getValue(JuelExpression.java:53)
	at org.activiti.engine.impl.el.UelExpressionCondition.evaluate(UelExpressionCondition.java:37)
	at org.activiti.engine.impl.bpmn.behavior.InclusiveGatewayActivityBehavior.execute(InclusiveGatewayActivityBehavior.java:63)
	at org.activiti.engine.impl.pvm.runtime.AtomicOperationActivityExecute.execute(AtomicOperationActivityExecute.java:60)
	at org.activiti.engine.impl.interceptor.CommandContext.performOperation(CommandContext.java:96)
	at org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:621)
	at org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperation(ExecutionEntity.java:616)
	at org.activiti.engine.impl.pvm.runtime.AtomicOperationTransitionNotifyListenerStart.eventNotificationsCompleted(AtomicOperationTransitionNotifyListenerStart.java:52)
	at org.activiti.engine.impl.pvm.runtime.AbstractEventAtomicOperation.execute(AbstractEventAtomicOperation.java:56)
	at org.activiti.engine.impl.interceptor.CommandContext.performOperation(CommandContext.java:96)
	at org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:621)
	at org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperation(ExecutionEntity.java:616)
	at org.activiti.engine.impl.pvm.runtime.AbstractEventAtomicOperation.execute(AbstractEventAtomicOperation.java:49)
	at org.activiti.engine.impl.interceptor.CommandContext.performOperation(CommandContext.java:96)
	at org.activiti.engine.impl.persistence.entity.ExecutionEntity.performOperationSync(ExecutionEntity.java:621)

请问，这是什么错