Is said whole, with nothing composed onto it and takes no だ/です, so there are no forms to conjugate.
そんなことはない
sonnakotohanaithat's not true; not at allexpression
Example sentences2
「太った?」「そんなことはないよ!」
"futotta?" "sonna koto wa nai yo!"
"Have you put on weight?" "Not at all!" casual
いいえ、そんなことはないと思います。
iie, sonna koto wa nai to omoimasu.
No, I don't think that's the case at all. neutral