Fix broken implementation of facet.missing support; basically, null keys

returned from solr weren't handled well at all.

@@ -159,6 +159,11 @@ define(function(require) {
                     return function facetItemValue(a, b) {
                         var keyA = sortKeyExtractor(a);
                         var keyB = sortKeyExtractor(b);
+                        if (keyA === null) {
+                            return -1;
+                        } else if (keyB === null) {
+                            return 1;
+                        }
                         return comparator.call(facet, keyA, keyB);
                     };
                 })(comparator);
@@ -282,12 +287,8 @@ define(function(require) {
                 } else if (excludeValues[key]) {
                     return;
                 }
-                var item = items.get({key: key});
-                if (item) {
-                    item.set({hidden: value === 0, value: value});
-                } else {
-                    item = new Facet.Item({key: key, value: value});
-                }
+                var item = this.getOrCreateItem(key);
+                item.set({hidden: value === 0, value: value});
                 newItems.push(item);
             }, this);
 
@@ -320,6 +321,20 @@ define(function(require) {
                 this.set({minValue: thisFacetStats.min, maxValue: thisFacetStats.max});
             }
         },
+        getOrCreateItem: function addOrGetItem(key) {
+            var items = this.get('items');
+            key = Facet.Item.checkNull(key);
+            var item = items.get(key);
+            if (!item) {
+                item = new Facet.Item({key: key, value: 0});
+            }
+            return item;
+        },
+        addOrGetItem: function addOrGetItem(key) {
+            var item = this.getOrCreateItem(key);
+            this.get('items').add(item);
+            return item;
+        },
         getFacetFormData: function(facetName, options) {
             options = options || {};
             var result = {
@@ -338,7 +353,10 @@ define(function(require) {
             var valueFormatter;
             var facetOptions = {};
             var quoteFormatter = function(value) {
-                return value.replace ? ('"' + value.replace(/"/, '\\"') + '"') : value;
+                if (value === 'null' || value === undefined || value === null) {
+                    return '(*:* -[\'\' TO *])';
+                }
+                return value && value.replace ? ('"' + value.replace(/"/, '\\"') + '"') : value;
             };
             var rangeFormatter = function(from, to) {
                 return '[' + quoteFormatter(from) + ' TO ' + quoteFormatter(to) + ']';
@@ -512,9 +530,35 @@ define(function(require) {
             }, this);
             return Item.__super__.initialize.apply(this, arguments);
         }
+    }, {
+        checkNull: function checkNull(value) {
+            return (value === 'null' || value === undefined) ? null : value;
+        },
     });
     var ItemCollection = Backbone.Collection.extend({
         model: Item,
+        initialize: function initialize(models, options) {
+            ItemCollection.__super__.initialize.apply(this, arguments);
+            this.on('update', function(model, options) {
+                var items = this;
+                _.each(options.changes.added, function(item) {
+                    if (!item.get('key')) {
+                        items._nullItem = item;
+                    }
+                });
+                _.each(options.changes.removed, function(item) {
+                    if (!item.get('key')) {
+                        delete items._nullItem;
+                    }
+                });
+            }, this);
+        },
+        get: function(obj) {
+            if (Item.checkNull(obj) === null) {
+                return this._nullItem;
+            }
+            return ItemCollection.__super__.get.apply(this, arguments);
+        },
         remove: function() {
         }
     });

@@ -88,16 +88,7 @@ define(function(require) {
                                 } else if (field === 'max') {
                                     impl.set('queryMax', parseInt(value), skipOptions);
                                 } else if (field === 'items') {
-                                    var items = impl.get('items');
-                                    var item = items.get(value);
-                                    if (!item) {
-                                        item = new Facets.Facet.Item({key: value, value: 0});
-                                        items.add(item);
-                                        item.on('change:checked', function(model, value, options) {
-                                            this.trigger('item-change', null, null, options);
-                                            impl.trigger('item-change', null, null, options);
-                                        }, facets);
-                                    }
+                                    var item = impl.addOrGetItem(value);
                                     item.set('checked', true, skipOptions);
                                 }
                             }