Maps ignore blocks at the lowest block position (y = -64 in the Overworld) with no block above

The bug

Maps ignore blocks at the lowest block position (y = -64 in the Overworld and y = 0 in other dimensions) if they do not have a transparent block (e.g. barrier or glass) above and show the default gray color instead.

How to reproduce

1. /fill ~ 0 ~ ~40 0 ~40 white_concrete
   

2. Create a map
   The map is gray instead of showing the white area