when `ProviderManager.SaveMetadata` gets called before
`ProviderManager.AddParts`
```
Error Message:
System.ArgumentNullException : Value cannot be null. (Parameter 'source')
Stack Trace:
at System.Linq.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument)
at System.Linq.Enumerable.Where[TSource](IEnumerable`1 source, Func`2 predicate)
at MediaBrowser.Providers.Manager.ProviderManager.SaveMetadata(BaseItem item, ItemUpdateType updateType, IEnumerable`1 savers) in D:\a\1\s\MediaBrowser.Providers\Manager\ProviderManager.cs:line 674
at MediaBrowser.Providers.Manager.ProviderManager.SaveMetadata(BaseItem item, ItemUpdateType updateType) in D:\a\1\s\MediaBrowser.Providers\Manager\ProviderManager.cs:line 655
at Emby.Server.Implementations.Library.LibraryManager.RunMetadataSavers(BaseItem item, ItemUpdateType updateReason) in D:\a\1\s\Emby.Server.Implementations\Library\LibraryManager.cs:line 2012
at Emby.Server.Implementations.Library.LibraryManager.UpdateItemsAsync(IReadOnlyList`1 items, BaseItem parent, ItemUpdateType updateReason, CancellationToken cancellationToken) in D:\a\1\s\Emby.Server.Implementations\Library\LibraryManager.cs:line 1970
at Emby.Server.Implementations.Library.LibraryManager.CreateRootFolder() in D:\a\1\s\Emby.Server.Implementations\Library\LibraryManager.cs:line 775
at Emby.Server.Implementations.Library.LibraryManager.get_RootFolder() in D:\a\1\s\Emby.Server.Implementations\Library\LibraryManager.cs:line 180
at Emby.Server.Implementations.IO.LibraryMonitor.Start() in D:\a\1\s\Emby.Server.Implementations\IO\LibraryMonitor.cs:line 135
at Emby.Server.Implementations.IO.LibraryMonitorStartup.RunAsync() in D:\a\1\s\Emby.Server.Implementations\IO\LibraryMonitorStartup.cs:line 26
at Emby.Server.Implementations.ApplicationHost.StartEntryPoints(IEnumerable`1 entryPoints, Boolean isBeforeStartup)+MoveNext() in D:\a\1\s\Emby.Server.Implementations\ApplicationHost.cs:line 541
at System.Threading.Tasks.Task.WhenAll(IEnumerable`1 tasks)
at Emby.Server.Implementations.ApplicationHost.RunStartupTasksAsync(CancellationToken cancellationToken) in D:\a\1\s\Emby.Server.Implementations\ApplicationHost.cs:line 525
at Jellyfin.Server.Integration.Tests.JellyfinApplicationFactory.CreateServer(IWebHostBuilder builder) in D:\a\1\s\tests\Jellyfin.Server.Integration.Tests\JellyfinApplicationFactory.cs:line 101
at Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory`1.EnsureServer()
at Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory`1.CreateDefaultClient(DelegatingHandler[] handlers)
at Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory`1.CreateDefaultClient(Uri baseAddress, DelegatingHandler[] handlers)
at Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory`1.CreateClient(WebApplicationFactoryClientOptions options)
at Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory`1.CreateClient()
at Jellyfin.Server.Integration.Tests.OpenApiSpecTests.GetSpec_ReturnsCorrectResponse() in D:\a\1\s\tests\Jellyfin.Server.Integration.Tests\OpenApiSpecTests.cs:line 26
--- End of stack trace from previous location ---
```
If the lookup fails (due to a bad id in an nfo file for example), then
we had no indication of which directory failed, so the user can not
fix the problem.
Now we include the path in the error message such as:
MediaBrowser.Providers.TV.SeriesMetadataService: Error in
DummySeasonProvider for /media/x/y/z
and
MediaBrowser.Providers.Manager.ProviderManager:
TvdbSeriesImageProvider failed in GetImageInfos for type Series at
/media/x/y/z
Add Argument*Exceptions now use proper nameof operators.
Added exception messages to quite a few Argument*Exceptions.
Fixed rethorwing to be proper syntax.
Added a ton of null checkes. (This is only a start, there are about 500 places that need proper null handling)
Added some TODOs to log certain exceptions.
Fix sln again.
Fixed all AssemblyInfo's and added proper copyright (where I could find them)
We live in *current year*.
Fixed the use of braces.
Fixed a ton of properties, and made a fair amount of functions static that should be and can be static.
Made more Methods that should be static static.
You can now use static to find bad functions!
Removed unused variable. And added one more proper XML comment.
