check for null completion node

pkg/analysis_server/lib/src/services/completion/dart_completion_manager.dart

Index: pkg/analysis_server/lib/src/services/completion/dart_completion_manager.dart
diff --git a/pkg/analysis_server/lib/src/services/completion/dart_completion_manager.dart b/pkg/analysis_server/lib/src/services/completion/dart_completion_manager.dart
index 54bb27d95477cc820be165c7aa5d68355a368cb2..3c20785973269ba49864e9b0730c12d4e791ec8c 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart_completion_manager.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart_completion_manager.dart
@@ -118,6 +118,9 @@ class DartCompletionManager extends CompletionManager {
       request.unit = unit;
       request.node = new NodeLocator.con1(request.offset).searchWithin(unit);
       request.target = new CompletionTarget.forOffset(unit, request.offset);
+      if (request.node == null) {
+        return [];
+      }
 
       request.replacementOffset = request.offset;
       request.replacementLength = 0;