Error with window fold

[Gyula Fóra]

Hey,

Running the following simple application gives me an error:

//just counting by key, the
streamOfIntegers.keyBy(x -> x).timeWindow(Time.milliseconds(3000)).fold(0, (
c, next) -> c + 1).print();

Executing this gives the following error:

"No initial value was serialized for the fold window function. Probably the
setOutputType method was not called."

Any idea?

Cheers,

Gyula