Fix issue 6945 (#6948)

CHANGES.md

@@ -41,6 +41,7 @@ Release Notes.
 * Fix: Envoy error logs are not persisted when no metrics are generated
 * Fix: Memory leakage of low version etcd client. [fix-issue](https://github.com/jurmous/etcd4j/pull/185)
 * Allow multiple definitions as fallback in metadata-service-mapping.yaml file.
+* Fix: NPE when configmap has no data. 
 
 #### UI
 * Add logo for kong plugin.

oap-server/server-configuration/configuration-k8s-configmap/src/main/java/org/apache/skywalking/oap/server/configuration/configmap/ConfigmapConfigurationWatcherRegister.java

@@ -42,7 +42,7 @@ public class ConfigmapConfigurationWatcherRegister extends ConfigWatcherRegister
         final ConfigTable configTable = new ConfigTable();
         Optional<V1ConfigMap> v1ConfigMap = informer.configMap();
         for (final String name : keys) {
-            final String value = v1ConfigMap.map(configMap -> configMap.getData().get(name)).orElse(null);
+            final String value = v1ConfigMap.map(V1ConfigMap::getData).map(data -> data.get(name)).orElse(null);
             if (log.isDebugEnabled()) {
                 log.debug("read config: name:{} ,value:{}", name, value);
             }

oap-server/server-configuration/configuration-k8s-configmap/src/test/java/org/apache/skywalking/oap/server/configuration/configmap/ConfigmapConfigWatcherRegisterTest.java

@@ -57,6 +57,19 @@ public class ConfigmapConfigWatcherRegisterTest {
         register = new ConfigmapConfigurationWatcherRegister(settings, informer);
     }
 
+    @Test
+    public void readConfigWhenConfigMapDataIsNull() throws Exception {
+        V1ConfigMap v1ConfigMap = new V1ConfigMap();
+        PowerMockito.doReturn(Optional.of(v1ConfigMap)).when(informer).configMap();
+        Optional<ConfigTable> optionalConfigTable = register.readConfig(new HashSet<String>() {{
+            add("key1");
+        }});
+
+        Assert.assertTrue(optionalConfigTable.isPresent());
+        ConfigTable configTable = optionalConfigTable.get();
+        Assert.assertEquals(configTable.getItems().size(), 0);
+    }
+
     @Test
     public void readConfigWhenInformerNotwork() throws Exception {
         PowerMockito.doReturn(Optional.empty()).when(informer).configMap();