WatchDocs null reference exception

[halcwb]

Describe the bug
When trying to 'watch' the docs, I got a null reference exception.

To Reproduce
Steps to reproduce the behavior:

1. Create a project using the template
2. Run the WatchDocs target
3. Refresh the browser after opening the docs page

Expected behavior
Reload of the page

Screenshots
The cmd line shows:

Hosting environment: Production
Content root path: C:\Development\lab\MiniScaffold\docsTool\bin\Debug\netcoreapp3.1
Now listening on: http://localhost:5000
Application started. Press Ctrl+C to shut down.
Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.
at Program.WebServer.openBrowser(String url) in C:\Development\lab\MiniScaffold\docsTool\Program.fs:line 510
at [email protected](Unit unitVar) in C:\Development\lab\MiniScaffold\docsTool\Program.fs:line 516
at Microsoft.FSharp.Control.AsyncPrimitives.CallThenInvoke[T,TResult](AsyncActivation1 ctxt, TResult result1, FSharpFunc2 part2) in E:\A_work\130\s\src\fsharp\FSharp.Core\async.fs:line 398
at Microsoft.FSharp.Control.Trampoline.Execute(FSharpFunc2 firstAction) in E:\A\_work\130\s\src\fsharp\FSharp.Core\async.fs:line 109 --- End of stack trace from previous location where exception was thrown --- at [email protected](ExceptionDispatchInfo edi) in E:\A\_work\130\s\src\fsharp\FSharp.Core\async.fs:line 907 at Microsoft.FSharp.Control.Trampoline.Execute(FSharpFunc2 firstAction) in E:\A_work\130\s\src\fsharp\FSharp.Core\async.fs:line 109
at Microsoft.FSharp.Control.TrampolineHolder.ExecuteWithTrampoline(FSharpFunc2 firstAction) in E:\A\_work\130\s\src\fsharp\FSharp.Core\async.fs:line 177 at <StartupCode$FSharp-Core>[email protected](Object o) in E:\A\_work\130\s\src\fsharp\FSharp.Core\async.fs:line 165 at System.Threading.QueueUserWorkItemCallback.<>c.<.cctor>b__6_0(QueueUserWorkItemCallback quwi) at System.Threading.ExecutionContext.RunForThreadPoolUnsafe[TState](ExecutionContext executionContext, Action1 callback, TState& state)
at System.Threading.QueueUserWorkItemCallback.Execute()
at System.Threading.ThreadPoolWorkQueue.Dispatch()
at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback()
watch : Exited with error code -532462766
watch : Waiting for a file to change before restarting dotnet...

Workaround
Wrapping the below code in a try catch resolves the issue:

    let openBrowser url =
        //https://github.com/dotnet/corefx/issues/10361
        try
            let psi = ProcessStartInfo(FileName = url, UseShellExecute = true)
            let proc = Process.Start psi
            proc.WaitForExit()
            if proc.ExitCode <> 0 then failwithf "opening browser failed"
        with
        | _ -> printfn "cannot open browser"

Desktop (please complete the following information):
.NET Core SDK (reflecting any global.json):
Version: 3.1.102
Commit: 573d158fea

Runtime Environment:
OS Name: Windows
OS Version: 10.0.18362
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\3.1.102\

Host (useful for support):
Version: 3.1.2
Commit: 916b5cba26

.NET Core SDKs installed:
2.1.801 [C:\Program Files\dotnet\sdk]
2.1.802 [C:\Program Files\dotnet\sdk]
2.2.401 [C:\Program Files\dotnet\sdk]
2.2.402 [C:\Program Files\dotnet\sdk]
3.0.100 [C:\Program Files\dotnet\sdk]
3.1.102 [C:\Program Files\dotnet\sdk]

Smartphone (please complete the following information):
NA

Additional context
Add any other context about the problem here.

[TheAngryByrd]

Maybe I should have followed the advice of the comment of that dotnet issue I have in that code 😂