SAFE template application fails to start when diagnostics are enabled

[bartsokol]

Steps to reproduce:

• Create new app using SAFE template with remoting enabled (dotnet new SAFE -lang F# --remoting)
• Try to build and start the app (build run)

Actual behaviour: server side (Saturn) application crashes with following exception:

Unhandled Exception: System.ArgumentException: The input sequence was empty.
Parameter name: source
   at Microsoft.FSharp.Collections.SeqModule.Last[T](IEnumerable`1 source)
   at Saturn.SiteMap.generate() in D:\Programowanie\Projekty\Saturn\Saturn\src\Saturn\Diagnostics.fs:line 55
   at Saturn.Application.run(IWebHostBuilder app) in D:\Programowanie\Projekty\Saturn\Saturn\src\Saturn\Application.fs:line 381
   at <StartupCode$Server>.$Server.main@() in C:\work\dotnet\SAFESample\src\Server\Server.fs:line 33

It looks like SiteMap.generate function is called on empty state. It should be updated with SiteMap.add function which seems to be never called.

Disabling diagnostics (using disable_diagnostics directive) solves the issue.

Environment: .NET Core SDK 2.1.300, Windows 10, Saturn 0.5

[Nhowka]

Maybe using Seq.tryLast could be safer with minimal changes.

[Krzysztof-Cieslak]

Fixed in ee03b96