Minor refactoring

Author: garrix-fan

src/main/java/io/confluent/kafka/connect/datagen/DatagenConnectorConfig.java

@@ -171,11 +171,11 @@ public void ensureValid(String name, Object value) {
       if (((String) value).isEmpty()) {
         return;
       }
-      if (!Quickstart.configValues.contains(((String) value).toLowerCase())) {
+      if (!Quickstart.configValues().contains(((String) value).toLowerCase())) {
         throw new ConfigException(String.format(
                 "%s must be one out of %s",
                 name,
-                String.join(",", DatagenTask.Quickstart.configValues)
+                String.join(",", DatagenTask.Quickstart.configValues())
         ));
       }
     }

src/main/java/io/confluent/kafka/connect/datagen/DatagenTask.java

@@ -87,7 +87,7 @@ protected enum Quickstart {
     STORES("stores.avro", "store_id"),
     CREDIT_CARDS("credit_cards.avro", "card_id");
 
-    static final Set<String> configValues;
+    private static final Set<String> configValues;
 
     static {
       ImmutableSet.Builder<String> immutableSetBuilder = ImmutableSet.builder();
@@ -106,6 +106,10 @@ protected enum Quickstart {
       this.keyName = keyName;
     }
 
+    public static Set<String> configValues() {
+      return configValues;
+    }
+
     public String getSchemaFilename() {
       return schemaFilename;
     }