Cannot `convert` an object of type DataValues.DataValue{Any} to an object of type DateTime

[IanButterworth]

I'm not sure if this is a core DataValues issue or one with the implementation in ExcelFiles or DataFrames (where I posted the same issue):
queryverse/ExcelFiles.jl#13
JuliaData/DataFrames.jl#1478

(I'll close the inappropriate issues once I figure out where the issue is)

I have dataframe df where column 1 is an array of DataValues.DataValue{Any}.
How can I convert it to DateTime, and allow for missing?

This doesn’t work:

datetimes = convert(Vector{Union{DateTime,Missing}}, df[1])

MethodError: Cannot `convert` an object of type DataValues.DataValue{Any} to an object of type DateTime

[IanButterworth]

Here's a concise example for testing:

using DataFrames, Dates, ExcelFiles
filename = "test.xlsx"
df = DataFrame(load(filename, string("Sheet1!A1:E25"),header=true))
df[:DateTime] = convert(Vector{Union{DateTime, Missing}},df[:DateTime])

And source excel file: https://www.dropbox.com/s/cwq5m6m9179s57a/test.xlsx?dl=1

[IanButterworth]

I've written a temporary function to fix the columns:

function fixcolumn(col,T)
    arr = Vector{Union{Missing, T}}(0)
    for x in col
        try
            push!(arr,x.value)
        catch
            push!(arr,missing)
        end
    end
    return arr
end

For instance:

df[:DateTime] = fixcolumn(df[:DateTime],DateTime)