The bug
MC-106747 suggests that the structure void block is supposed to be a map making block only. Because of that I would expect piston to be unable to break it.
Linked issues
Comments
SunCat
marcono1234
Sorry did not see that report. Kind of strange considering MC-106747 was fixed.
You can break the structure void in survival (see MC-102908), so it's not an indestructible block.