How to randomize the values in a table?

[Fixed it by myself]

Tried this, works sometimes, sometimes fails..

local Difficulties = {"Hard","Easy","Normal"}
table.sort(Difficulties, function(a,b)
return math.random() > 0.5
end)
print(table.concat(Difficulties, ' '))

Error: 13:17:48.509 - Workspace.Script:5: invalid value (nil) at index 1 in table for 'concat'