F# passing none to function, getting null as parameter value

Question

This is really weird and I fear I have just done something dumb but I can't figure it out. I'm passing `None` to the function `some` as the first parameter but when the function executes, the value of `parentNode` is null (I'm not concerned with it printing null for `None`, the function parameter value IS null not `None`). I end up getting a null reference error on the print function line because parentNode is null. I've tried to tuple the args and change the order but that didn't help. I have a sneaking suspicion that this has something to do with currying but I'm at a loss... I had to replace the real url value with an empty string for company issues but it is a url to an xsd if that helps Here is the code: ``` #light open System open System.Xml open System.Net open System.Collections.Generic type StartResult = | Parameters of XsdParserParameters | Xsd of Xsd and Xsd(text) = let rows = new List<string>() member this.Text with get() = text member this.Rows with get() = rows and XsdPa…

Accepted Answer

Unfortunately, it's the way F# prints out `None`:

```
> sprintf "%O" None;;
val it : string = "<null>"
```

You can easily write a custom `sprintf` function for `option` type, for example:

```
let sprintOption v = 
    if Option.isNone v then "None" else sprintf "%A" v
```

F# passing none to function, getting null as parameter value

Solution

Problem