Unless it is good question (1+ vote) closing with one duplicate and comment about another should be enough. OP has info and if question ends up with negative score it will be cleaned by Roomba later.
In most cases I've seen similar behavior OP ignores all available debugging guidance and posts question with NRE (which indeed asks for duplicate of "What is NRE and how to fix it") instead of figuring out that whole/partial model passed in as null in controller.
If you feel generous you can edit question to clarify that root cause of NRE is binding (also it may be hard without building whole project), but it is hard to recommend as general approach as it does not scale.
My recommendation: if OP failed to debug root cause of NRE - closing as duplicate of "What is NRE and how to fix it" is perfectly valid and give OP chance to debug code and update post with extra information. At that point question can be re-opened and closed as correct duplicate.
If OP already provided clear information where null comes from - closing as duplicate of "What is NRE" is uncalled for and commenting to close voters may be better approach. Especially if close was done by gold badge holder it should be trivial to ask to re-open.
If question does not look worth fighting for (most of those are about the same - wrong naming) adding comment "Root cause is duplicate of ...." or "You can find more info by searching for {list of keywords}". There is really no huge difference for most of posters if question is duplicate of one or another question.
