in(::Missing, ::Any) inconsistency

[nsajko]

julia> missing ∈ ()
false

julia> missing ∈ (7,)
missing

julia> missing ∈ Set(7)
false

julia> missing ∈ []
false

julia> missing ∈ [7]
missing

julia> missing ∈ Int[]
false

julia> versioninfo()
Julia Version 1.12.0-DEV.489
Commit 29ced9e2a02 (2024-05-08 07:57 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 8 × AMD Ryzen 3 5300U with Radeon Graphics
  WORD_SIZE: 64
  LLVM: libLLVM-17.0.6 (ORCJIT, znver2)
Threads: 6 default, 0 interactive, 6 GC (on 8 virtual cores)

Currently ∈ behaves in a weird manner when it's first argument is missing. It sometimes returns missing and sometimes false. But I guess it never returns true. The result depends both on collection type and emptiness status.

Some of these results are featured in the doc string...

[martinholters]

But I guess it never returns true.

julia> missing ∈ [missing]
missing

julia> missing ∈ Set([missing])
true