word without root

Could cybalist members help me in resolving a puzzle?

It is a Russian verb " vynut' " ("to take out").
vy- is prefix, -t' is infinitive ending. If we look at the verb's conjugation:
1sg: vynu
2sg: vynesh'
3sg: vynet
-nu- looks like common verbal suffix (reduced in future forms to -n-).
That leaves no space for the root.

I could guess that original structure was vy-n-im-ti (with -n- inserted by
analogy with prefixes vUn-, sUn-), then by analogy with large group of verb
on -nu, -nim- was replaced with suffix -nu and thus the verb eventually
lost its root. Is it correct? If it is, are there other examples of
"rootless" words?

Regards,
Andrei