// reading not existing attribute of /
ModelNode operation = new ModelNode();
operation.get(ADDRESS).set(new ModelNode());
operation.get(NAME).set("notexisting");
operation.get(OP).set(READ_ATTRIBUTE_OPERATION);

dispatcher.execute(new DMRAction(operation), new LoggingCallback<DMRResponse>() {
    public void onSuccess(DMRResponse response) {
        ModelNode outcome = response.get().get(ModelDescriptionConstants.OUTCOME);
        if(outcome.asString().equals(ModelDescriptionConstants.SUCCESS)){
            // ...
        }else{
            // **This will be executed in GWT debug mode**
        }
    }
    public void onFailure(Throwable caught) {
        // **This will be executed in production**
    }
});