Fix NPE in transform method

Author: Yunyung

clients/src/main/java/org/apache/kafka/common/config/AbstractConfig.java

@@ -624,6 +624,7 @@ private Map<String, Plugin<ConfigProvider>> instantiateConfigProviders(
         Map<String, Plugin<ConfigProvider>> configProviderPluginInstances = new HashMap<>();
         for (Map.Entry<String, String> entry : providerMap.entrySet()) {
             try {
+                System.out.println("Checking:" + entry);
                 String prefix = CONFIG_PROVIDERS_CONFIG + "." + entry.getKey() + CONFIG_PROVIDERS_PARAM;
                 Map<String, ?> configProperties = configProviderProperties(prefix, providerConfigProperties);
                 ConfigProvider provider = Utils.newInstance(entry.getValue(), ConfigProvider.class);

clients/src/main/java/org/apache/kafka/common/config/ConfigTransformer.java

@@ -96,13 +96,13 @@ public ConfigTransformerResult transform(Map<String, String> configs) {
         Map<String, Long> ttls = new HashMap<>();
         for (Map.Entry<String, Map<String, Set<String>>> entry : keysByProvider.entrySet()) {
             String providerName = entry.getKey();
-            ConfigProvider provider = configProviderPlugins.get(providerName).get();
+            Plugin<ConfigProvider> providerPlugin = configProviderPlugins.get(providerName);
             Map<String, Set<String>> keysByPath = entry.getValue();
-            if (provider != null && keysByPath != null) {
+            if (providerPlugin != null && keysByPath != null) {
                 for (Map.Entry<String, Set<String>> pathWithKeys : keysByPath.entrySet()) {
                     String path = pathWithKeys.getKey();
                     Set<String> keys = new HashSet<>(pathWithKeys.getValue());
-                    ConfigData configData = provider.get(path, keys);
+                    ConfigData configData = providerPlugin.get().get(path, keys);
                     Map<String, String> data = configData.data();
                     Long ttl = configData.ttl();
                     if (ttl != null && ttl >= 0) {