C#: Address C# code comments.

Author: criemen

csharp/extractor/Semmle.Extraction/Extractor/Extractor.cs

@@ -109,7 +109,7 @@ public static string Version
             {
                 // the attribute for the git information are always attached to the entry assembly by our build system
                 var assembly = Assembly.GetEntryAssembly();
-                var versionString = assembly!.GetCustomAttribute<AssemblyInformationalVersionAttribute>();
+                var versionString = assembly?.GetCustomAttribute<AssemblyInformationalVersionAttribute>();
                 if (versionString == null)
                 {
                     return "unknown (not built from internal bazel workspace)";

csharp/extractor/Testrunner/Testrunner.cs

@@ -63,23 +63,25 @@ private void OnTestSkipped(TestSkippedInfo info)
     public int RunTests()
     {
         var assembly = Assembly.GetExecutingAssembly();
-        var testrunner = AssemblyRunner.WithoutAppDomain(assembly.Location);
-        testrunner.OnDiscoveryComplete = OnDiscoveryComplete;
-        testrunner.OnExecutionComplete = OnExecutionComplete;
-        testrunner.OnTestFailed = OnTestFailed;
-        testrunner.OnTestSkipped = OnTestSkipped;
-
-        Console.WriteLine("Discovering tests...");
-        testrunner.Start(parallelAlgorithm: null);
-
-        Finished.WaitOne();
-        Finished.Dispose();
-
-        // Wait for assembly runner to finish.
-        // If we try to dispose while runner is executing,
-        // it will throw an error.
-        while (testrunner.Status != AssemblyRunnerStatus.Idle)
-            Thread.Sleep(100);
+        using (var testrunner = AssemblyRunner.WithoutAppDomain(assembly.Location))
+        {
+            testrunner.OnDiscoveryComplete = OnDiscoveryComplete;
+            testrunner.OnExecutionComplete = OnExecutionComplete;
+            testrunner.OnTestFailed = OnTestFailed;
+            testrunner.OnTestSkipped = OnTestSkipped;
+
+            Console.WriteLine("Discovering tests...");
+            testrunner.Start(parallelAlgorithm: null);
+
+            Finished.WaitOne();
+            Finished.Dispose();
+
+            // Wait for assembly runner to finish.
+            // If we try to dispose while runner is executing,
+            // it will throw an error.
+            while (testrunner.Status != AssemblyRunnerStatus.Idle)
+                Thread.Sleep(100);
+        }
         return Result;
     }