NullReferenceException using String.Contains

f#

Solution

Try adding a call to `System.String.IsNullOrEmpty` into your `List.filter` and see if it fixes the problem:

pdfLinks
|> List.filter(fun x ->
    (not <| System.String.IsNullOrEmpty x) &&
    x.Contains("shop"))
|> List.iter (printfn "%s")

Problem

I don't know why I'm getting that Exception on the List.filter part of the following code: ``` pdfLinks |> List.filter(fun x -> x.Contains("shop")) |> List.iter (printfn "%s") ``` pdfLinks is of type "string list" and it is populated with tons of strings that contain the word "shop". It works ok in F# Interactive with a dummy list. The original one has been generated by parsing an HTML file but inspecting it by a watch shows it has desired values of the desired type. Any idea what may be happening? Thanks!

Original source