Support nullable objects in the RequestBuilder.param() method

[arbue]

Hi,

is there a way to pass nullable values to the param method so that it is not included in the serialized string as a null value.

If there is no existing way could you add a new method to the RequestBuilder class which for example just skips setting null values to the newObjectParams object.

   @NotNull
    public RequestBuilder<T> paramNullable(@NotNull String name, Object value) {
        ObjectNode newObjectParams = objectParams.deepCopy();
        if(value != null){
            newObjectParams.set(name, mapper.valueToTree(value));
        }
        return new RequestBuilder<T>(transport, mapper, method, id, newObjectParams, arrayParams, javaType);
    }

I could also provide a PR with that change if you like.