I just noticed this line in the System Preferences app on OS X:
Click the lock to make changes
Here, に is put after a verb's plain form. I have never seen this kind of usage before. As far as I know, に is a 格助詞. And 格助詞 don't connect to verbs. They only connect to 体言, which I think does not include verbs.
So i searched online to see if this is a usage that I am not aware of. And I found this. But that does not show any examples of this "verb plain form + に" usage.
It also says that
格助詞 is mainly put after a noun and shows the relationship between that noun and another noun, a verb used as a predicate or an adjective.
How can に be put after a verb's plain form? What is this usage?