On Mon, 24 Jul 2017, William Schilp wrote:

The java object is held by the 'jobject this$' member variable in the C++
wrapper. I think that if Java returned a null object, this$ is set to 0;

You might also be able to use the '!' operator declared on JObject:

     inline int operator!() const
         return env->isSame(this$, NULL);

if (!wrapper)  // java returned null