ray ignoring specific materials?

I've found out that if you have a ray detecting terrain but nothing else then it only ever prints enum.Material.Air, so is there any such way to ignore specific enum.Material so that I don't have to try and mess with the ray locations so it automatically hits the terrain instead of the of the air.

Although I'm using the outdated raycast system, it wouldn't be the issue, because it actually function unlike the new version.

So is there any such way to ignore specific materials?