Bringing Unity 4 to Unity 5 with its lightmaps

I've looked, but there doesn't seem to be any documentations out there or anyone who is asking the same thing.

I have some scenes that is lit in the Unity 4 and I need to bring it to Unity 5, for all sorts of reasons other than lighting. The issue at hand is Unity doesn't attach my old lightmaps when it upgrades a project nor does it does it create lightmap slots to browse for old maps.

I don't know of any way to create lightmap slots other than to finish a bake. However, even with no setting change it generates new lightmaps and atlas the UVs differently thus breaking the old lightsmaps.

Can you reattach old lightmaps and without breaking the old atlas UVs?

 

As far as I know it was mentioned in the last release that Unity 4 lighmaps won't work in Unity 5 anymore. Which means you have to re-bake each scene in Unity 5 using the new system.