Leave "error" key out of response JSON when there is no error.

pkg/analysis_server/lib/src/protocol.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 protocol;
 
 import 'dart:convert' show JsonDecoder;
 
 /**
  * Instances of the class [Request] represent a request that was received.
@@ skipping 394 matching lines @@
     result[name] = value;
   }
 
   /**
    * Return a table representing the structure of the Json object that will be
    * sent to the client to represent this response.
    */
   Map<String, Object> toJson() {
     Map<String, Object> jsonObject = new Map<String, Object>();
     jsonObject[ID] = id;
-    if (error == null) {
-      jsonObject[ERROR] = null;
-    } else {
+    if (error != null) {
       jsonObject[ERROR] = error.toJson();
     }
     if (!result.isEmpty) {
       jsonObject[RESULT] = result;
     }
     return jsonObject;
   }
 }
 
 /**
@@ skipping 16 matching lines @@
   /**
    * The name of the JSON attribute containing a short description of the error.
    */
   static const String MESSAGE = 'message';
 
   /**
    * An error code indicating a parse error. Invalid JSON was received by the
    * server. An error occurred on the server while parsing the JSON text.
    */
   static const int CODE_PARSE_ERROR = -32700;
-  
+
   /**
    * An error code indicating that the analysis server has already been
    * started (and hence won't accept new connections).
    */
   static const int CODE_SERVER_ALREADY_STARTED = -32701;
 
   /**
    * An error code indicating an invalid request. The JSON sent is not a valid
    * [Request] object.
    */
@@ skipping 51 matching lines @@
    * the JSON text.
    */
   RequestError.parseError() : this(CODE_PARSE_ERROR, "Parse error");
 
   /**
    * Initialize a newly created [Error] to indicate that the analysis server
    * has already been started (and hence won't accept new connections).
    */
   RequestError.serverAlreadyStarted()
     : this(CODE_SERVER_ALREADY_STARTED, "Server already started");
-  
+
   /**
    * Initialize a newly created [Error] to indicate an invalid request. The
    * JSON sent is not a valid [Request] object.
    */
   RequestError.invalidRequest() : this(CODE_INVALID_REQUEST, "Invalid request");
 
   /**
    * Initialize a newly created [Error] to indicate that a method was not found.
    * Either the method does not exist or is not currently available.
    */
@@ skipping 158 matching lines @@
   /**
    * The response to be returned as a result of the failure.
    */
   final Response response;
 
   /**
    * Initialize a newly created exception to return the given reponse.
    */
   RequestFailure(this.response);
 }