Rss importer fails when RSS entry is empty

When the RSS importer runs on an empty RSS feed (which can happen), it fails and it cannot process the other RSS feeds.

Example of empty RSS feeds:

<feed xmlns="http://www.w3.org/2005/Atom" xml:lang="en">
  <id>https://www.example.com/rss</id>
  <title>Example</title>
  <updated>2023-07-27T15:25:42.947430+00:00</updated>
  <link href="https://www.example.com/rss"/>
  <generator uri="https://lkiesow.github.io/python-feedgen" version="0.9.0">python-feedgen</generator>
</feed>

Stack trace:

2023-07-27 15:14:09.5670 [INFO] [DocIntel.Core.Importers.RSSSourceImporter] Collecting RSS feed for 'Example' (870175bc-f9c7-402b-96cd-ceb8ac506ecf)
2023-07-27 15:14:09.5755 [ERROR] [DocIntel.Services.Importer.Runner] System.InvalidOperationException
2023-07-27 15:14:09.5755 [ERROR] [DocIntel.Services.Importer.Runner] Sequence contains no elements
   at System.Linq.ThrowHelper.ThrowNoElementsException()
   at System.Linq.Enumerable.Max[TSource,TResult](IEnumerable`1 source, Func`2 selector)
   at DocIntel.Core.Importers.RSSSourceImporter.PullAsync(Nullable`1 lastPull, Int32 limit)+MoveNext() in /src/DocIntel.Core/Importers/RSSSourceImporter.cs:line 154
   at DocIntel.Core.Importers.RSSSourceImporter.PullAsync(Nullable`1 lastPull, Int32 limit)+System.Threading.Tasks.Sources.IValueTaskSource<System.Boolean>.GetResult()
   at DocIntel.Services.Importer.Runner.CollectFeed(Importer feed, AmbientContext feedContext) in /src/DocIntel.Services.Importer/Runner.cs:line 137
   at DocIntel.Services.Importer.Runner.CollectFeed(Importer feed, AmbientContext feedContext) in /src/DocIntel.Services.Importer/Runner.cs:line 137
   at DocIntel.Services.Importer.Runner.ImportFeeds() in /src/DocIntel.Services.Importer/Runner.cs:line 102
   at DocIntel.Services.Importer.Runner.RunAsync(CancellationToken cancellationToken) in /src/DocIntel.Services.Importer/Runner.cs:line 80

Analysis of the issue:

in DocIntel.Core\Importers\RSSSourceImporter.cs
line 139: rssMetadata.LastPull = feed.Items.Max(_ => _.PublishDate).DateTime;

=> there should be a check if feed.Items is empty or not before executing this line

docintelapp / DocIntel

Rss importer fails when RSS entry is empty #87