How do I hard wire a T8 fluorescent light fixture with grounded plug to a motion sensor?
Your light fixture has hot, neutral, and ground.

The diagram actually shows the switched hot and neutral connecting to the light - ground is or should be obvious, it's not shown probably to reduce clutter.

As shown on the diagram, you connect the neutral from the wires supplying the location of the sensor to the fixture wire. It does not connect to the sensor at all. As not shown, you do the same thing with the ground. As shown, you connect the switched hot to the fixture.