Fix `NullPointerException` in Istio ServiceEntry registry (#12087)

docs/en/changes/changes.md

@@ -93,6 +93,7 @@
     - API `/api/v1/labels` and `/api/v1/label/<label_name>/values` support return matched metrics labels.
   - OAL:
     - Deprecate `percentile` function and introduce `percentile2` function instead.
+* Fix `NullPointerException` in Istio ServiceEntry registry.
 
 #### UI
 

oap-server/server-receiver-plugin/envoy-metrics-receiver-plugin/src/main/java/org/apache/skywalking/oap/server/receiver/envoy/als/istio/IstioServiceEntryRegistry.java

@@ -74,6 +74,10 @@ public class IstioServiceEntryRegistry {
                     .filter(se -> !ignoredNamespaces.contains(se.getMetadata().getNamespace()))
                     .filter(se -> {
                         final var spec = se.getSpec();
+                        if (spec.getResolution() == null) {
+                            log.debug("Unsupported service entry resolution: {}", spec.getResolution());
+                            return false;
+                        }
                         switch (spec.getResolution()) {
                             case STATIC:
                                 return spec