[FIXED] Lua / attempt to index local 'a' (a nil value)

Hello everyone. I am new to lua and would like if someone could see what causes my problem… So i was looking at a tutorial so i could do my first ever game. But i get an error that the man i followed didn’t had.

(Using Love2D btw)

main.lua:21: attempt to index local ‘a’ (a nil value)

Issue :
function checkCollision(a, b)
if a.x + a.width > b.x and a.x < b.x + b.width and a.y + a.height > b.y and a.y < b.y + b.height then
return true
else
return false
end
end

Actually, Fixed. Looked at his source code and fixed it.