Minor Observatory UI tweaks.

runtime/observatory/lib/src/elements/eval_box.dart

 // Copyright (c) 2013, 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 eval_box_element;
 
 import 'dart:async';
 import 'dart:html';
 import 'observatory_element.dart';
 import 'package:polymer/polymer.dart';
 
 
 typedef Future evalType(String text);
 
 
 @CustomTag('eval-box')
 class EvalBoxElement extends ObservatoryElement {
   @observable String text;
   @observable String lineMode = "1-line";
   int _exprCount = 0;
 
   @published evalType callback;
   @observable ObservableList results = toObservable([]);
 
   void updateLineMode(Event e, var detail, Node target) {
     lineMode = (e.target as InputElement).value;
-    if (lineMode == '1-line') {
+    if (lineMode == '1-line' && text != null) {
       text = text.replaceAll('\n', ' ');
     }
   }
 
   void evaluate(Event e, var detail, Node target) {
     // Prevent any form action.
     e.preventDefault();
 
     // Clear the text box.
     var expr = text;
@@ skipping 22 matching lines @@
 
   void closeItem(MouseEvent e) {
     assert(e.target is Element);
     Element targetElement = e.target;
     var closeId = targetElement.getAttribute('closeId');
     results.removeWhere((item) => item['id'] == closeId);
   }
 
   EvalBoxElement.created() : super.created();
 }