More nullable fixes

StabilityMatrix.Avalonia/Controls/CodeCompletion/CompletionList.cs

@@ -502,7 +502,11 @@ public class CompletionList : TemplatedControl
         if (string.IsNullOrEmpty(query))
             return;
 
-        var suggestedIndex = _listBox.SelectedIndex;
+        var suggestedIndex = _listBox?.SelectedIndex ?? -1;
+        if (suggestedIndex == -1)
+        {
+            return;
+        }
 
         var bestIndex = -1;
         var bestQuality = -1;

StabilityMatrix.Avalonia/DesignData/MockLiteDbContext.cs

@@ -47,7 +47,7 @@ public class MockLiteDbContext : ILiteDbContext
 
     public Task<GithubCacheEntry?> GetGithubCacheEntry(string cacheKey)
     {
-        return Task.FromResult<GithubCacheEntry>(null);
+        return Task.FromResult<GithubCacheEntry?>(null);
     }
 
     public Task<bool> UpsertGithubCacheEntry(GithubCacheEntry cacheEntry)

StabilityMatrix.Core/Models/Packages/BaseGitPackage.cs

@@ -239,8 +239,13 @@ public abstract class BaseGitPackage : BasePackage
     public override async Task<bool> CheckForUpdates(InstalledPackage package)
     {
         var currentVersion = package.Version;
-        if (currentVersion == null)
+        if (currentVersion is null or { InstalledReleaseVersion: null, InstalledBranch: null })
         {
+            Logger.Warn(
+                "Could not check updates for package {Name}, version is invalid: {@currentVersion}",
+                Name,
+                currentVersion
+            );
             return false;
         }
 
@@ -254,7 +259,7 @@ public abstract class BaseGitPackage : BasePackage
             }
 
             var allCommits = (
-                await GetAllCommits(currentVersion.InstalledBranch).ConfigureAwait(false)
+                await GetAllCommits(currentVersion.InstalledBranch!).ConfigureAwait(false)
             )?.ToList();
             if (allCommits == null || !allCommits.Any())
             {