热点参数修改问题

spring-cloud-starter-alibaba-sentinel 2.2.5.RELEASE
com.alibaba.csp 1.8.0

需求：将 `resource=/test/test03/` 的数据count=3改为count=2

报错：

```
java.lang.NullPointerException
at com.alibaba.csp.sentinel.slots.block.flow.param.ParamFlowRuleManager$RulePropertyListener.aggregateAndPrepareParamRules(ParamFlowRuleManager.java:141)
at com.alibaba.csp.sentinel.slots.block.flow.param.ParamFlowRuleManager$RulePropertyListener.configUpdate(ParamFlowRuleManager.java:103)
at com.alibaba.csp.sentinel.slots.block.flow.param.ParamFlowRuleManager$RulePropertyListener.configUpdate(ParamFlowRuleManager.java:99)
at com.alibaba.csp.sentinel.property.DynamicSentinelProperty.updateValue(DynamicSentinelProperty.java:57)
at com.alibaba.csp.sentinel.slots.block.flow.param.ParamFlowRuleManager.loadRules(ParamFlowRuleManager.java:54)
at com.alibaba.csp.sentinel.command.handler.ModifyParamFlowRulesCommandHandler.handle(ModifyParamFlowRulesCommandHandler.java:58)
at com.alibaba.csp.sentinel.transport.command.http.HttpEventTask.run(HttpEventTask.java:103)
```

sentinel-dashboard发送更新热点参数请求

```
curl -X POST 'http://10.16.50.244:18401/setParamFlowRules' --header 'Content-Type: application/x-www-form-urlencoded' --data-urlencode 'data=[{"burstCount":0,"clusterConfig":{"fallbackToLocalWhenFail":true,"flowId":16,"sampleCount":10,"thresholdType":1,"windowIntervalMs":1000},"clusterMode":true,"controlBehavior":0,"count":2.0,"durationInSec":1,"grade":1,"limitApp":"default","maxQueueingTimeMs":0,"paramFlowItemList":[{"classType":"java.lang.String","count":1,"object":"1"}],"paramIdx":0,"resource":"/test/test03/*"}]'
```

sentinel客户端应用，ParamFlowRuleManager.loadRules()方法接收处理，在DynamicSentinelProperty.updateValue()方法中value = newValue;将新值赋给旧值，ParamFlowRuleManager.aggregateAndPrepareParamRules()方法，oldRuleList.removeAll(newRuleList);这里期望将新的值从旧的列表中删除，可是新值count=2，旧值count=3，故删除不了这也是问题的根本原因，接下来代码ParameterMetricStorage.getParamMetricForResource(resource).clearForRule(rule);报null，故修改失败，因为之前value = newValue;，所以ParamFlowRuleManager.PARAM_FLOW_RULES中的数据还是旧值，而全部变量value是新值，数据不一致。

我现在的解决思路：重写ParamFlowRuleManager.aggregateAndPrepareParamRules()方法逻辑，重写DynamicSentinelPropert。updateValue()方法，如果失败，保证value值还是旧值

Start with ParamFlowRuleManager.loadRules() and its RulePropertyListener.aggregateAndPrepareParamRules() path, then inspect DynamicSentinelProperty.updateValue() and the referenced ParameterMetricStorage cleanup. Reproduce the count change from 3 to 2 using the reported request and stack trace. Done means the update no longer throws a NullPointerException and the new rule value is applied consistently.

Written by the indexing model from the issue text.