If the gyro Vector3dF passed to ElbowModel::Update is (0, 0, 0), the pointer and reticle in VR Shell are no longer rendered. This shouldn't be an issue during actual use unless someone's trying to use VR Shell in zero gravity, but it causes the pointer to be missing during automated tests if using the automated emulated Daydream controller.

Works fine if at least one element is non-zero. My initial guess is that the length of the vector is being calculated somewhere, and when it's zero, causes math errors, as the beam_direction vector in vr_shell_gl.cc is (nan, nan, nan) in this case.