Interop with libraries written in csharp

interop.fs

let dependencies (package : IPackage) =
    match package.DependencySets with
    | null -> []
    | sets -> 
        sets
        |> filterNulls
        |> Seq.map (fun d -> d.Dependencies)
        |> filterNulls
        |> Seq.concat
        |> filterNulls
        |> Seq.filter (fun x -> x.VersionSpec <> null)
        |> Seq.toList