collect(powerset(::Set)) doesn't work

powerset(::Set) works, but returns Iterator.
```julia
julia> s
Set{Char} with 3 elements:
'a'
'c'
'b'

julia> collect(powerset(s))
ERROR: MethodError: no method matching getindex(::Set{Char}, ::Int64)
```

`collect(powerset(collect(s)))` works as expected though.

I think it'd be nice to be able to work with set theory without syntactic issues like this, particularly for pedagogic purposes.

edit: sorry accidentally pressed enter and it made the issue.