SceneKit nodesInsideFrustumWithPointOfView: unexpectedly returning empty - ios

Question

I am using the following method to determine which SCNNodes are visible by the camera.
[self.scnView nodesInsideFrustumWithPointOfView:cameraNode];
However the returned array is always empty.
I set up the scene up as follows:
-(void)setupScene{
scene = [SCNScene scene];
cameraNode = [SCNNode node];
cameraNode.camera = [SCNCamera camera];
[scene.rootNode addChildNode:cameraNode];
cameraNode.position = SCNVector3Make(0, 0, 0);
[scene.rootNode addChildNode:cameraNode];
self.scnView.scene = scene;
self.scnView.showsStatistics = YES;
self.scnView.backgroundColor = [UIColor clearColor];
}
At a random time, after the scene is created, I add a SCNNode to the scene:
testnode = [Testnode createNode];
testnode.position = SCNVector3Make(0, 0, -10);
[self.scnView.scene.rootNode addChildNode:testnode];
On my device, the node "testnode" is visible on my screen yet nodesInsideFrustumWithPointOfView: returns nothing.
EDIT: I tried changing the point of view to a spot light object and test whether "testnode" is inside its frustum. Here is what I see on screen: http://imgur.com/a/C3XGu Yet the array still returns empty. The testnode is the white cube.

Answer 1

Adding this for better visibility. Thank Crashalot for this.
Basically, if the SCNNode you are trying to detect using [scnView nodesInsideFrustumWithPointOfView:] and [scnView isNodeInsideFrustum: withPointOfView:] is the child of a node with empty geometry, it won't be detected.
In my case, I added a plane geometry and set the material to transparent:
SCNNode *emptynode = [SCNNode node];
node.geometry = [SCNPlane planeWithWidth:1.0f height:2.0f];
node.geometry.firstMaterial.transparency = 0.0f;