Fix NPE in rename local (issue 25933)

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

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library services.src.refactoring.rename_local;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/protocol_server.dart' hide Element;
 import 'package:analysis_server/src/services/correction/status.dart';
@@ skipping 132 matching lines @@
         conflictingLocals.add(nodeElement);
         String nodeKind = nodeElement.kind.displayName;
         String message = "Duplicate $nodeKind '$newName'.";
         result.addError(message, newLocation_fromElement(nodeElement));
         return;
       }
       if (conflictingLocals.contains(nodeElement)) {
         return;
       }
       // shadowing referenced element
-      if (elementRange.contains(node.offset) &&
+      if (elementRange != null &&
+          elementRange.contains(node.offset) &&
           !node.isQualified &&
           !_isNamedExpressionName(node)) {
         nodeElement = getSyntheticAccessorVariable(nodeElement);
         String nodeKind = nodeElement.kind.displayName;
         String nodeName = getElementQualifiedName(nodeElement);
         String nameElementSourceName = nodeElement.source.shortName;
         String refKind = refactoring.element.kind.displayName;
         String message = 'Usage of $nodeKind "$nodeName" declared in '
             '"$nameElementSourceName" will be shadowed by renamed $refKind.';
         result.addError(message, newLocation_fromNode(node));
       }
     }
   }
 
   static bool _isNamedExpressionName(SimpleIdentifier node) {
     return node.parent is Label && node.parent.parent is NamedExpression;
   }
 }