Means the trace doesn’t hit anything. It might be hard to see in my screenshot, but it’s important the Z value linked into the Line Trace’s Start input hook is greater than the one Z value linked into the End hook. So the trace shoots from (above) your object to below the floor.
Just how high above the ground is your door placed? You could try increasing the second value passed into the Minus node.
Alternatively, the floor gets ignored by the Trace check. This should work for both StaticMeshes or Landscape. Does it have collision? What are its Collision Presets settings in the Details panel?