Fix NPE in rename local (issue 25933)

pkg/analysis_server/lib/src/services/refactoring/rename_local.dart

Index: pkg/analysis_server/lib/src/services/refactoring/rename_local.dart
diff --git a/pkg/analysis_server/lib/src/services/refactoring/rename_local.dart b/pkg/analysis_server/lib/src/services/refactoring/rename_local.dart
index 4f1f150c22502d5ca8c04dd3f7d295fb73db6423..e161a437244e03b64c925973c88bc9d06b9f3833 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/rename_local.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/rename_local.dart
@@ -150,7 +150,8 @@ class _ConflictValidatorVisitor extends RecursiveAstVisitor {
         return;
       }
       // shadowing referenced element
-      if (elementRange.contains(node.offset) &&
+      if (elementRange != null &&
+          elementRange.contains(node.offset) &&
           !node.isQualified &&
           !_isNamedExpressionName(node)) {
         nodeElement = getSyntheticAccessorVariable(nodeElement);