Mmap(io, Vector{Union{Missing,T}}, ...)

Is there a way I can mmap a vector of eltype Union{Missing, T} where isbits(T)? Clearly !isbits(Union{Missing, T}), but I thought this had a compact memory representation now.

OK if it works only in v0.7.

As a workaround, can I mmap the missingness mask and the data separately, and somehow combine them into the above for the interface?

Opened an issue: