Why does this ray casting code with the ignore list not work?

Why doesn't this work? It's supposed to make it so it only prints on grass, but it doesn't print at all?

local Ignorelist = {}
local descendants = workspace:GetDescendants()
for index, descen in pairs(descendants) do
    if not Ignorelist[descen.Name] then
        if descen.ClassName == "Part" or descen.ClassName == "MeshPart" or descen.ClassName == "Union" then
            if descen.Material == "Grass" then
                table.insert(Ignorelist, descen.Name)
            end
        end
    end
end
local ray = Ray.new(HumanoidRootPart.Position,Vector3.new(0,-10,0))
local part, endPoint, Normal, Material = workspace:FindPartOnRayWithIgnoreList(ray, Ignorelist)
if part then
    print(part.Name)
end