URL RESTful service working, but in ANDROID returns null

I'm trying to develop a rest service for my dad's store, I'm getting the results in JSON through the URL, but when I try executor the same method in android to try to fill the object, it returns null, I've debugged and I can go so the method that does the SELECT in the bank, it brings the right list, filled .. The problem is on the side of the android, I can not map the result ... Does anyone know what can be ?? !!

Here are the methods:

public List<Produto> getProdutosPromocionais(boolean promocional, double preco) {
    return ClienteRest.builder().path("produtos").path("promocionais").path(promocional).path(preco).build().listar(Produto.class);
}

    @GET
    @Path("/promocionais/{promocional}/{preco}")
    @AddLinks
    public List<Produto> getProdutosPromocionais(@PathParam("promocional") boolean promocional, @PathParam("preco") double preco) {
        return servico.getProdutosPromocionais(promocional, preco);
    }

the query is correct, the URL works, but on the android side it returns NULL ..