[Bug]: Reloading a page or opening a deep link without a loaded file must not crash  #58

What type of issue is this?

• Bug report
• Feature request

Prerequisites

• I have written a descriptive issue title
• I have verified that I am running the latest version of the reqifviewer
• I have searched open and closed issues to ensure it has not already been reported

Description

The loaded file lives in server memory per connection. Opening a shared link, or reloading any page such as /reqif/{id}/specobjects, gives a 500 error: ArgumentNullException: Value cannot be null. (Parameter 'source') in SpecObjectsComponent.OnParametersSet.

Acceptance criteria

• Every page handles "no document loaded" or "unknown identifier": it shows a friendly message with a button to open a file, instead of a 500 error.
• Tests: each page rendered with an empty IReqIFLoaderService.
• With [Feature]: Decide on, and if chosen, move to Blazor WebAssembly hosting  #64 (WebAssembly) the document can be restored after a reload; without it, the message explains that files are not kept on the server.

Steps to Reproduce

Load requirements-and-objects.reqifz or ProR_Traceability-Template-v1.0.reqif (reqifviewer.Tests/TestData) and look at the pages mentioned above.

System Configuration

• reqifviewer version: 6.1.0 (development, with [Refactor] Blazor Blueprint app shell and Blazor Web App hosting #56)
• Environment (Operating system, version and so on): Windows 11, Chrome
• .NET Framework version: .NET 10
• Additional information: Plan item F-02 of the viewer improvement plan. Size: S.