private static String constructorCacheKey(String builderName, String name, Class<?> currentClass) {
        return builderName + "." + name + "." + currentClass.getName();
    }
Finds a nested class with the given <code>name</code>name in <code>clazz</code>.

@param clazz a Class
@param name a name
@return class found, or null if no class is found
config/src/main/java/com/yahoo/vespa/config/ConfigPayloadApplier.java