Tinkerpop Frames writing to database - newbie

I'm having my first go with Frames and my Java is pretty rusty. I'm stuck on writing information through Frames into the database. I've been following the docs and have a Person interface.

public interface Person {
  @Property("name")
  public String getName();

  @Adjacency(label="knows")
  public Iterable<Person> getKnowsPeople();

  @Adjacency(label="knows")
  public void addKnowsPerson(final Person person);

  @GremlinGroovy("it.out('knows').out('knows').dedup") //Make sure you use the GremlinGroovy module! #1
  public Iterable<Person> getFriendsOfAFriend()
}

Which is taken from the docs. I can use this simple code to get data out of the graph.

TinkerGraph graph = TinkerGraphFactory.createTinkerGraph(); //This graph is pre-populated.
FramedGraphFactory factory = new FramedGraphFactory(new GremlinGroovyModule()); //(1) Factories should be reused for performance and memory conservation.

FramedGraph framedGraph = factory.create(graph); //Frame the graph.

Person person = framedGraph.getVertex(1, Person.class);
person.getName(); // equals "marko"

What I'd like to know is how I would create a new Person object and write it to the graph. Because Person is only an interface I can't do:

Person person2 = new Person();
person2.setName("John");
person2.setAge(36);
framedGraph.addVertex(person2);

So I've tried a PersonImpl class which implements Person and added the following code

PersonImpl johnBoy = new PersonImpl();
johnBoy.setName("John");
johnBoy.setAge(36);
johnBoy.addKnowsPerson(person);
person.addKnowsPerson(johnBoy);

However I'm getting the following NullPointer and I'm now really stuck. I was hoping someone might possibly be able to help me.

Exception in thread "main" java.lang.NullPointerException
    at com.tinkerpop.blueprints.impls.tg.TinkerGraph.addEdge(TinkerGraph.java:331)
    at com.tinkerpop.frames.FramedGraph.addEdge(FramedGraph.java:310)
    at com.tinkerpop.frames.annotations.AdjacencyAnnotationHandler.addEdges(AdjacencyAnnotationHandler.java:87)
    at com.tinkerpop.frames.annotations.AdjacencyAnnotationHandler.processVertex(AdjacencyAnnotationHandler.java:53)
    at com.tinkerpop.frames.annotations.AdjacencyAnnotationHandler.processElement(AdjacencyAnnotationHandler.java:26)
    at com.tinkerpop.frames.annotations.AdjacencyAnnotationHandler.processElement(AdjacencyAnnotationHandler.java:15)
    at com.tinkerpop.frames.FramedElement.invoke(FramedElement.java:89)
    at com.sun.proxy.$Proxy4.addKnowsPerson(Unknown Source)
    at com.elecrticdataland.utility.TinkerTest.main(TinkerTest.java:45)

With many thanks,

John

You can't create a Person except by way of proxy. In other words, you can't use a concrete implementation of that interface, it has to be constructed dynamically by the FramesGraph.

You have the code to create a Person here:

FramedGraph framedGraph = factory.create(graph); //Frame the graph.

Person person = framedGraph.getVertex(1, Person.class);
person.getName(); // equals "marko"

Without that, the created Person implementation will not know anything about the underlying and injected Graph instance given to factory.create()