How to migrate version of PooledArrays inside JLD2 file

General Usage
4

Ok, so I came up with this solution that gets rid of the PooledArrays dependency altogether:

using FileIO, DataFrames, PooledArrays, SentinelArrays

if length(ARGS) == 0
    println("Usage: convert_pooled_arrays.jl <jld file>...")
    exit(-1)
end

for f in ARGS
    expec = load(f)
    changed = false
    for k in keys(expec)
        if isa(expec[k], AbstractDataFrame)
            for col in names(expec[k])
                if isa(expec[k][!, col], PooledArrays.PooledArray)
                    println(f, ": ", k, ".", col)
                    expec[k][!, col] = Vector{eltype(expec[k][!, col])}(expec[k][!, col])
                    changed = true
                end
            end
        end
    end
    if changed
        save(f, expec; compress=true)
    end
end