Any can mean "everything" or "none".
Let me explain; Any friend of yours is a friend of mine = Each /every single friend of yours is a friend of mine.
It hasn't anything to do with singular or plural. "Any" can be positive or negative.
Example: How many friends do you have ? ... I don't have any !
In the latter you see that this is a rather negative use of the word "any".
Kind Regards ... ps: I do have friends
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