What can I use to replace .As() in my function?

Question

This Deedle function used to work:

let firstNonSparseRow (df: Frame<'K,'S>) : ('K*Series<'S,'a>) option =
        Frame.rows df
        |> (fun s -> s.As())
        |> Series.observations
        |> Seq.tryFind (snd >> Series.hasNoMissing)

Now I get the compiler message:

error FS0039: The type 'RowSeries<_,_>' does not define the field, constructor or member 'As'.

I was expecting the function to work and return the first row not containing missing or None.

I tried several variations of the code above, none worked.