Dictionary / Vocabulary / 無きにしもあらず
なきにしもあらず
not non-existent; not completely lacking; there is some; certainly existent
Also written 無きにしも非ず
トムが言ってることも、無きにしも非ず。でもね、メアリーが言ってることの方が筋が通ってるよね。
What Tom is saying is not completely incorrect. What Mary is saying makes a lot more sense though.