How do you handle unknown POINT values in MySQL?

[Peter Barney]

I posted this in the InnoDB forum, but I think this is probably a better place for my question.

MySQL 5.7 introduced Spatial Indexes on POINT columns. Apparently, you cannot have NULL values in a spatial index. At the same time, you cannot use a DEFAULT for POINT columns.

So how do you handle the case where the value for POINT is unknown?

I geocode every address in my database, but if the end user doesn't supply an address, what should I put there?

In another question, someone suggested placing them at the North Pole POINT(0.0000,90.0000) but this takes 25 bytes for each unknown address.

Is there a way to resolve this?

FYI: I am not a DBA.