I get what you mean, but using a word with a very specific meaning in a legal context to mean something else that's similar and likewise in a legal context, but

I get what you mean, but using a word with a very specific meaning in a legal context to mean something else that's similar and likewise in a legal context, but with a more vague definition, will just create confusion. This kind of confusion in a legal context can cause major problems for people when they're trying to understand the law as it applies to their case. I don't think calling this nullification even adds any "spirit" meaning that isn't already present in "the grand jury declined to indict". These two things can be similar, but the details matter here.