updated comments

src/Features/Core/Portable/SolutionCrawler/WorkCoordinator.cs

@@ -74,7 +74,8 @@ private partial class WorkCoordinator
                     _registration.Workspace.DocumentClosed += OnDocumentClosed;
                 }
 
-                // subscribe to option changed event
+                // subscribe to option changed event after all required fields are set
+                // otherwise, we can get null exception when running OnOptionChanged handler
                 _optionService.OptionChanged += OnOptionChanged;
             }