private Constructor<?> getStructBuilderConstructor(Class<?> structClass, String currentClassName, String builderName) {
        String structBuilderName = currentClassName + "$" + builderName + "$Builder";
        Class<?> structBuilderClass = getInnerClass(structClass, structBuilderName);
        if (structBuilderClass == null)
            throw new RuntimeException("Could not find builder class " + structBuilderName);
        try {
            return structBuilderClass.getDeclaredConstructor();
        } catch (NoSuchMethodException e) {
            throw new RuntimeException("Could not create class '" + "'" + structBuilderClass.getName() + "'");
        }
    }
Checks if this field is of type 'path', in which
case some special handling might be needed. Caches the result.
config/src/main/java/com/yahoo/vespa/config/ConfigPayloadApplier.java