Explicitly return null if there aren't any results

IPython/html/static/notebook/js/widgetmanager.js

@@ -1,185 +1,186
 //----------------------------------------------------------------------------
 //  Copyright (C) 2013  The IPython Development Team
 //
 //  Distributed under the terms of the BSD License.  The full license is in
 //  the file COPYING, distributed as part of this software.
 //----------------------------------------------------------------------------
 
 //============================================================================
 // WidgetModel, WidgetView, and WidgetManager
 //============================================================================
 /**
  * Base Widget classes
  * @module IPython
  * @namespace IPython
  * @submodule widget
  */
 
 (function () {
     "use strict";
 
     // Use require.js 'define' method so that require.js is intelligent enough to
     // syncronously load everything within this file when it is being 'required' 
     // elsewhere.
     define(["underscore",
              "backbone",
             ], function (Underscore, Backbone) {
 
         //--------------------------------------------------------------------
         // WidgetManager class
         //--------------------------------------------------------------------
         var WidgetManager = function (comm_manager) {
             // Public constructor
             WidgetManager._managers.push(this);
 
             // Attach a comm manager to the 
             this.comm_manager = comm_manager;
             this._models = {}; /* Dictionary of model ids and model instances */
 
             // Register already-registered widget model types with the comm manager.
             _.each(WidgetManager._model_types, function(value, key) {
                 this.comm_manager.register_target(value, $.proxy(this._handle_comm_open, this));
             });
         };
 
         //--------------------------------------------------------------------
         // Class level
         //--------------------------------------------------------------------
         WidgetManager._model_types = {}; /* Dictionary of model type names (target_name) and model types. */
         WidgetManager._view_types = {}; /* Dictionary of view names and view types. */
         WidgetManager._managers = []; /* List of widget managers */
 
         WidgetManager.register_widget_model = function (model_name, model_type) {
             // Registers a widget model by name.
             WidgetManager._model_types[model_name] = model_type;
 
             // Register the widget with the comm manager.  Make sure to pass this object's context
             // in so `this` works in the call back.
             _.each(WidgetManager._managers, function(instance, i) {
                 if (instance.comm_manager !== null) {
                     instance.comm_manager.register_target(model_name, $.proxy(instance._handle_comm_open, instance));
                 }
             });
         };
 
         WidgetManager.register_widget_view = function (view_name, view_type) {
             // Registers a widget view by name.
             WidgetManager._view_types[view_name] = view_type;
         };
 
         //--------------------------------------------------------------------
         // Instance level
         //--------------------------------------------------------------------
         WidgetManager.prototype.display_view = function(msg, model) {
             var cell = this.get_msg_cell(msg.parent_header.msg_id);
             if (cell === null) {
                 console.log("Could not determine where the display" + 
                     " message was from.  Widget will not be displayed");
             } else {
                 var view = this.create_view(model, {cell: cell});
-                if (view === undefined) {
+                if (view === null) {
                     console.error("View creation failed", model);
                 }
                 if (cell.widget_subarea !== undefined
                     && cell.widget_subarea !== null) {
                     
                     cell.widget_area.show();
                     cell.widget_subarea.append(view.$el);
                 }
             }
         },
 
         WidgetManager.prototype.create_view = function(model, options) {
             var view_name = model.get('view_name');
             var ViewType = WidgetManager._view_types[view_name];
             if (ViewType !== undefined && ViewType !== null) {
                 var parameters = {model: model, options: options};
                 var view = new ViewType(parameters);
                 view.render();
                 IPython.keyboard_manager.register_events(view.$el);
                 model.views.push(view);
                 model.on('destroy', view.remove, view);
                 return view;
             }
+            return null;
         },
 
         WidgetManager.prototype.get_msg_cell = function (msg_id) {
             var cell = null;
             // First, check to see if the msg was triggered by cell execution.
             if (IPython.notebook !== undefined && IPython.notebook !== null) {
                 cell = IPython.notebook.get_msg_cell(msg_id);
             }
             if (cell !== null) {
                 return cell
             }
             // Second, check to see if a get_cell callback was defined
             // for the message.  get_cell callbacks are registered for
             // widget messages, so this block is actually checking to see if the
             // message was triggered by a widget.
             var kernel = this.comm_manager.kernel;
             if (kernel !== undefined && kernel !== null) {
                 var callbacks = kernel.get_callbacks_for_msg(msg_id);
                 if (callbacks !== undefined && 
                     callbacks.iopub !== undefined && 
                     callbacks.iopub.get_cell !== undefined) {
 
                     return callbacks.iopub.get_cell();
                 }    
             }
             
             // Not triggered by a cell or widget (no get_cell callback 
             // exists).
             return null;
         };
 
         WidgetManager.prototype.callbacks = function (view) {
             // callback handlers specific a view
             var callbacks = {};
             var cell = view.options.cell;
             if (cell !== null) {
                 // Try to get output handlers
                 var handle_output = null;
                 var handle_clear_output = null;
                 if (cell.output_area !== undefined && cell.output_area !== null) {
                     handle_output = $.proxy(cell.output_area.handle_output, cell.output_area);
                     handle_clear_output = $.proxy(cell.output_area.handle_clear_output, cell.output_area);
                 }
 
                 // Create callback dict using what is known
                 var that = this;
                 callbacks = {
                     iopub : {
                         output : handle_output,
                         clear_output : handle_clear_output,
 
                         // Special function only registered by widget messages.
                         // Allows us to get the cell for a message so we know
                         // where to add widgets if the code requires it.
                         get_cell : function () {
                             return cell;
                         },
                     },
                 };
             }
             return callbacks;
         };
 
         WidgetManager.prototype.get_model = function (model_id) {
             var model = this._models[model_id];
             if (model !== undefined && model.id == model_id) {
                 return model;
             }
             return null;
         };
 
         WidgetManager.prototype._handle_comm_open = function (comm, msg) {
             var model_id = comm.comm_id;
             var widget_type_name = msg.content.target_name;
             var widget_model = new WidgetManager._model_types[widget_type_name](this, model_id, comm);
             this._models[model_id] = widget_model;
         };
         
         IPython.WidgetManager = WidgetManager;
         return IPython.WidgetManager;
     });
 }());