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

「太ふとった?」「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おもいます。

iie, sonna koto wa nai to omoimasu.

No, I don't think that's the case at all. neutral