Guard against getting a watch event before the driver is created (issue 30333)

pkg/analysis_server/lib/src/context_manager.dart

Index: pkg/analysis_server/lib/src/context_manager.dart
diff --git a/pkg/analysis_server/lib/src/context_manager.dart b/pkg/analysis_server/lib/src/context_manager.dart
index 008ab6139f49895d535460b6c0b2fe465ebbbb60..7a6c0b99fd8b5da8e34bc9ebecdc09979255e46b 100644
--- a/pkg/analysis_server/lib/src/context_manager.dart
+++ b/pkg/analysis_server/lib/src/context_manager.dart
@@ -919,11 +919,14 @@ class ContextManagerImpl implements ContextManager {
       String contextRoot = info.folder.path;
       ContextBuilder builder =
           callbacks.createContextBuilder(info.folder, defaultContextOptions);
-      AnalysisOptions options = builder.getAnalysisOptions(contextRoot,
-          contextRoot: info.analysisDriver?.contextRoot);
-      SourceFactory factory = builder.createSourceFactory(contextRoot, options);
       AnalysisDriver driver = info.analysisDriver;
-      driver.configure(analysisOptions: options, sourceFactory: factory);
+      if (driver != null) {
+        AnalysisOptions options = builder.getAnalysisOptions(contextRoot,
+            contextRoot: driver.contextRoot);
+        SourceFactory factory =
+            builder.createSourceFactory(contextRoot, options);
+        driver.configure(analysisOptions: options, sourceFactory: factory);
+      }
     }
   }