nodata设置了agent.alive为-1
agent正常运行，其他监测项都能采集，唯独agent.alive一直为-1。
测试后，发现endpoint配置到nodata中，就一直返回的是-1，如果不配置到nodata中，可正常返回1。这是什么原因呢？
Windows agent日志：
[Debug]2019/07/23 18:22:05 listening :1988
[Debug]2019/07/23 18:23:05 IIs Monitor is disabled
[Debug]2019/07/23 18:23:05 MsSQL Monitor is disabled
[Debug]2019/07/23 18:23:07 => <Total=34> <Endpoint:web-01, Metric:agent.alive, Type:GAUGE, Tags:, Step:60, Time:1563877387, Value:1>
[Debug]2019/07/23 18:23:07 <= <Total=34, Invalid:0, Latency=0ms, Message:ok>
[Debug]2019/07/23 18:24:05 IIs Monitor is disabled
[Debug]2019/07/23 18:24:05 MsSQL Monitor is disabled
[Debug]2019/07/23 18:24:06 => <Total=34> <Endpoint:web-01, Metric:agent.alive, Type:GAUGE, Tags:, Step:60, Time:1563877446, Value:1>
[Debug]2019/07/23 18:24:06 <= <Total=34, Invalid:0, Latency=0ms, Message:ok>
[Debug]2019/07/23 18:25:05 IIs Monitor is disabled
[Debug]2019/07/23 18:25:05 MsSQL Monitor is disabled
[Debug]2019/07/23 18:25:06 => <Total=34> <Endpoint:web-01, Metric:agent.alive, Type:GAUGE, Tags:, Step:60, Time:1563877506, Value:1>
[Debug]2019/07/23 18:25:06 <= <Total=34, Invalid:0, Latency=0ms, Message:ok>
[Debug]2019/07/23 18:26:05 IIs Monitor is disabled
[Debug]2019/07/23 18:26:05 MsSQL Monitor is disabled
[Debug]2019/07/23 18:26:06 => <Total=34> <Endpoint:web-01, Metric:agent.alive, Type:GAUGE, Tags:, Step:60, Time:1563877566, Value:1>
[Debug]2019/07/23 18:26:06 <= <Total=34, Invalid:0, Latency=0ms, Message:ok>
[Debug]2019/07/23 18:27:05 IIs Monitor is disabled
[Debug]2019/07/23 18:27:05 MsSQL Monitor is disabled
[Debug]2019/07/23 18:27:06 => <Total=34> <Endpoint:web-01, Metric:agent.alive, Type:GAUGE, Tags:, Step:60, Time:1563877626, Value:1>
[Debug]2019/07/23 18:27:06 <= <Total=34, Invalid:0, Latency=0ms, Message:ok>
nodata设置了agent.alive为-1
agent正常运行，其他监测项都能采集，唯独agent.alive一直为-1。
测试后，发现endpoint配置到nodata中，就一直返回的是-1，如果不配置到nodata中，可正常返回1。这是什么原因呢？
Windows agent日志：
[Debug]2019/07/23 18:22:05 listening :1988
[Debug]2019/07/23 18:23:05 IIs Monitor is disabled
[Debug]2019/07/23 18:23:05 MsSQL Monitor is disabled
[Debug]2019/07/23 18:23:07 => <Total=34> <Endpoint:web-01, Metric:agent.alive, Type:GAUGE, Tags:, Step:60, Time:1563877387, Value:1>
[Debug]2019/07/23 18:23:07 <= <Total=34, Invalid:0, Latency=0ms, Message:ok>
[Debug]2019/07/23 18:24:05 IIs Monitor is disabled
[Debug]2019/07/23 18:24:05 MsSQL Monitor is disabled
[Debug]2019/07/23 18:24:06 => <Total=34> <Endpoint:web-01, Metric:agent.alive, Type:GAUGE, Tags:, Step:60, Time:1563877446, Value:1>
[Debug]2019/07/23 18:24:06 <= <Total=34, Invalid:0, Latency=0ms, Message:ok>
[Debug]2019/07/23 18:25:05 IIs Monitor is disabled
[Debug]2019/07/23 18:25:05 MsSQL Monitor is disabled
[Debug]2019/07/23 18:25:06 => <Total=34> <Endpoint:web-01, Metric:agent.alive, Type:GAUGE, Tags:, Step:60, Time:1563877506, Value:1>
[Debug]2019/07/23 18:25:06 <= <Total=34, Invalid:0, Latency=0ms, Message:ok>
[Debug]2019/07/23 18:26:05 IIs Monitor is disabled
[Debug]2019/07/23 18:26:05 MsSQL Monitor is disabled
[Debug]2019/07/23 18:26:06 => <Total=34> <Endpoint:web-01, Metric:agent.alive, Type:GAUGE, Tags:, Step:60, Time:1563877566, Value:1>
[Debug]2019/07/23 18:26:06 <= <Total=34, Invalid:0, Latency=0ms, Message:ok>
[Debug]2019/07/23 18:27:05 IIs Monitor is disabled
[Debug]2019/07/23 18:27:05 MsSQL Monitor is disabled
[Debug]2019/07/23 18:27:06 => <Total=34> <Endpoint:web-01, Metric:agent.alive, Type:GAUGE, Tags:, Step:60, Time:1563877626, Value:1>
[Debug]2019/07/23 18:27:06 <= <Total=34, Invalid:0, Latency=0ms, Message:ok>