Fix potential NPE bug when updating ParamFlowRule before the resource has been requested once (#1901)

sentinel-extension/sentinel-parameter-flow-control/src/main/java/com/alibaba/csp/sentinel/slots/block/flow/param/ParamFlowRuleManager.java

@@ -138,7 +138,10 @@ public final class ParamFlowRuleManager {
                 List<ParamFlowRule> oldRuleList = new ArrayList<>(entry.getValue());
                 oldRuleList.removeAll(newRuleList);
                 for (ParamFlowRule rule : oldRuleList) {
-                    ParameterMetricStorage.getParamMetricForResource(resource).clearForRule(rule);
+                    ParameterMetric parameterMetric = ParameterMetricStorage.getParamMetricForResource(resource);
+                    if (parameterMetric != null) {
+                        parameterMetric.clearForRule(rule);
+                    }
                 }
             }
 

sentinel-extension/sentinel-parameter-flow-control/src/test/java/com/alibaba/csp/sentinel/slots/block/flow/param/ParamFlowRuleManagerTest.java

@@ -138,4 +138,18 @@ public class ParamFlowRuleManagerTest {
         assertTrue(allRules.contains(ruleC));
         assertTrue(allRules.contains(ruleD));
     }
+
+    @Test
+    public void testLoadParamRulesWithNoMetric() {
+        String resource = "test";
+        ParamFlowRule paramFlowRule = new ParamFlowRule(resource)
+                .setDurationInSec(1).setParamIdx(1);
+        ParamFlowRuleManager.loadRules(Collections.singletonList(paramFlowRule));
+        ParamFlowRule newParamFlowRule = new ParamFlowRule(resource)
+                .setDurationInSec(2).setParamIdx(1);
+        ParamFlowRuleManager.loadRules(Collections.singletonList(newParamFlowRule));
+        List<ParamFlowRule> result = ParamFlowRuleManager.getRulesOfResource(resource);
+        assertEquals(1, result.size());
+        assertEquals(2, result.get(0).getDurationInSec());
+    }
 }